Download Chronic inflammation

Chronic inflammation
By Dr. S Homathy
Chronic inflammation
• Inflammation of prolonged duration(weeks to
months to year)
• In which
– acute inflammation,
– tissue injury and
– healing
• proceed simultaneously
Components of chronic inflammation
1.Acute inflammation
2.Demolition
3.Healing – repair and regeneration
4.Immune response
It is characterized by
 Infiltration with mononuclear (‘chronic inflammatory’)
cells, including
– Macrophage
– Lymphocytes
– Plasma cells
 Tissue destruction
– Largely directed by inflammatory cells
 Repair
– Involving new vessel proliferation( angiogenesis and fibrosis)
• 1.Acute inflammation
– Evidence of acute inflammation is frequently seen
in chronic inflammation
Eg: pus rich in neutrophils in
osteomyelitis, pyonephrosis, chronic brain abscess
: exudates rich in Eosinophils in hypersensitivity reaction
• 2.Demolition
– Accomplished by macrophages derived from
emigrating monocytes of bone marrow origin
• 3.Healing
– Repair
• New vessel formation (angiogenesis)
• Fibrosis (dense fibrosis and loss of function)
– Regeneration
• Clearance of injurious stimuli
• Clearance of mediators and chronic inflammatory cells
• Regeneration and remodeling of damaged tissue
• Normal function
Eg : surface epithelia
• 4.Immune response
– Very common feature is the accumulation of
lymphocytes of various types, plasma cells, and
MP.
– Plasma immunoglobins levels may be elevated.
Chronic inflammation
can occur
•
Following acute inflamation
•
Starting de novo
or
Differ from AI
•
•
•
•
•
•
Absence of cardinal signs
New vessel formation
No fluid exudation or oedema
Time is prolonged
Immune response
Injurious agents most often cause insidious,
progressive and often extensive tissue necrosis
• Accompanied by ongoing repair by fibrosis
• Specific ( immune response is activated)
• Systemic response – low grade fever, weight loss,
anaemia
Causes of chronic inflammation
• Viral infections
– Intracellular infection of any kind require lymphocytes
and macrophages
• To identify and eradicate infected cells.
• Persistent microbial infections
– By some specific organisms
Eg: Mycobacteria, Treponema pallidum, certain fungi
– Organisms are low direct pathogenicity
– Typically evoke an immune response- delayed
hypersensitivity
• Persistent injury
– Prolonged exposure to potentially toxic agents
Eg : silica produce -silicosis of lung
: chronically elevated plasma lipids- produce
Atherosclerosis
• Autoimmune diseases
– Immune response to self- antigen and tissues
Eg: Rheumatoid arthritis / multiple sclerosis.
The Players (mononuclear
phagocyte system)
• Macrophages
– Scattered all over
•
•
•
•
Microglia - CNS
Kupffer cells - liver
sinus histiocytes – spleen , lymphnode
alveolar macrophages - lungs.
– Circulate as monocytes
– reach site of injury within 24 – 48 hrs and
transform into large macrophages
– Large MP now capable of phagocytosis
– Become activated by T cell-derived cytokines,
endotoxins, and other products of inflammation
• Greater ability to kill ingested organisms
LM appearance with H&E stain
• Large
• Flat
• Pink
– Similar to squamous cell ( called epithelioid
macrophages)
• After activation, MP secretes a wide variety of
biologically active products
• If unchecked leads to tissue injury and fibrosis
• Mediaters from MP
– Acid and neutral proteases
– Complement and coagulation factors
• C1 to c5
• Propedin
• Coaguulation factor V and VIII
– Reactive oxygen speces and NO
– AA metabolites
– CK
• In CI MP accumulation persist and MP can
proliferate
• lymphocytes derived factors recruit or
immobilize the MP to the site of injury
• IL-4 or INF-γ
– Causes MP to fuse into large, multinucleated cells
• Called giant
cells
• T and B lymphocytes
– Antigen-activated (via macrophages and dendritic
cells)
– Release macrophage-activating cytokines (in turn,
macrophages release lymphocyte-activating
cytokines until inflammatory stimulus is removed)
• Plasma cells
– Terminally differentiated B cells
– Produce antibodies
• Eosinophils
– Found especially at sites of parasitic infection, or
at
– allergic (IgE-mediated) sites
• Mast cells
– Participate in both acute and chronic inflammatory
responses
– Armed with IgE to certain antigens
• Chronic endometritis withlymphocytes as well
as plasma cells in the endometrial stroma.
• In general, the inflammatory infiltrate of chronic
inflammation consists mainly of mononuclear cells
("round cells"):
– lymphocytes, plasma cells, and macrophages.
Chronic cervicitis.
• Prolonged acute inflammation or repeated bouts of acute
inflammation may lead to the appearance of
– more mononuclear cells,
– and chronic inflammation.
• In this case the inflammation is severe enough to produce mucosal
damage with hemorrhage.
• Chronic inflammation can go on for a long time:
– weeks to months to years.
• Seen here in the synovium from the joint of a patient
with rheumatoid arthritis are
– collections of dark blue lymphocytes.
Types of chronic inflammation
• Granulomatous chronic inflmmation
• Non- granulomatous chronic inflammation
Granulomatous inflammation
Definition:
• Granulomatous inflammation is a distinctive
pattern of chronic inflammatory reaction.
• It is a protective response to chronic infection or
foreign material, preventing dissemination and
restricting inflammation.
• Some autoimmune diseases such as Crohns
disease is also associated with granulomas.
Cellular constituents of Granulomas
• the predominant cell type is an activated
macrophage with a modified epithelial-like
(epithelioid) appearance
• Lymphocytes.
• Occasional plasma cells
What Is A Granuloma?
• A granuloma is a microscopic aggregation of
macrophages that
– are transformed into epithelium-like cells surrounded
by
– a collar of mononuclear leukocytes,
• principally lymphocytes and occasionally plasma cells.
– Older granulomas also develop a surrounding rim of
fibroblast and connective tissue
• Due to CK elaborated by the activated MP
– Frequently, but not invariably multinucleated giant
cells are also found
• Derived from fusion of 20 or more MP
• These are epithelioid cells around the center of a
granuloma.
• They get their name from the fact that they have lots of
pink cytoplasm similar to squamous epithelial cells.
• Their nuclei tend to be long and stringy
• Epithelioid cells fuse to form giant cells
containing 20 or more nuclei.
• These giant cells can be found either at the
periphery or the center of the granuloma
Types of giant cells
• The nuclei arranged either
– Peripherally
• Langhans-type giant cell
(Reaction to certain organism)
– haphazardly
• foreign body-type giant cell
(reaction to insoluble materials)
– Nuclei enclose the central part of the homogeneous
eosinophilic cytoplasm and the peripheral part of the
cytoplasm is vacuolated due to its lipid content
• Touton giant cell
(found in xanthomas)
• MP found in Rheumatic heart disease also
called caterpillar cells, as they have a large
amount of clear cytoplasm surrounding a rodshaped nucleus that to some resembles a
caterpillar.
• Larger Anitschkow cells may coalesce to form
multinucleated Aschoff giant cells
• Nuclears appears as amirror image of one
another
– Reed-sternberg giant cell found in Hodgkin’s
lymphoma
• Fibrous connective tissue often surrounds
granulomas (remodeling of tissue)
• Areas within the granuloma can undergo
necrosis
– prototype: caseous necrosis in tuberculosis.
• Granular, cheesy
– Necrosis can lead to calcification or liquefaction
and formation of a cavern if drained.
CAUSES OF GRANULOMATOUS
DISEASES
Infectious causes:
• Bacteria
–
–
–
–
Tuberculosis
Leprosy(tuberculod type)
Trepanema pallidum
Brucella species
• Rickttsial organism
– Coxiella burnetii
• Parasites
– Schistosomiasis
• Fungi
• Histoplasmosis
• Blastomycosis
• coccidioidomycosis
Metal/Dust
• Berylliosis
• Silicosis
• Foreign body Granulomas:
– endogenous
( keratin, necrotic bone or adipose tissue uric acid
crystals)
– Exogenous
(wood, silica, asbestos, silicone,suture…)
• Specific chemicals:
– Beryllium
•
unknown cause
– Sarcoidosis
– Crohn’s disease
Type of granulomas
1. Foreign body granulomas
–
form when material such as talc, sutures, or
other fibers are large enough to preclude
phagocytosis by a single macrophage.
2. Epithelioid granuloma (Immune
granulomas )
• caused by insoluble particles that are capable
of inducing a cell-mediated response.
• This type of immune response produces
granulomas when the inciting agent is poorly
soluble or particulate.
• Macrophages
–
–
–
–
–
engulf the foreign material and
process and
present some of it to appropriate T lymphocytes,
causing them to become activated,
responding T cells produce cytokines,
• such as IL-2
– which activates other T cells and
• IFN-
– which is important in transforming macrophages into epithelioid
cells and multinucleate giant cells.
•Here is a foreign body type giant cell at the upper left of center
•adjacent to a segment of vegetable material aspirated into the
lung.
• Such foreign body giant cells have nuclei scattered haphazardly
about the cell
•Two foreign body
giant cells are seen
•just to the right of
center
•where there is a bluish
strand of suture
material from a
previous operation
• Granulomatous disease can become quite
extensive.
• Here are numerous confluent granulomas in
upper lung fields in a case of active pulmonary
tuberculosis.
Grossly,
• a granuloma tends to be a focal lesion.
• Seen here in a hilar lymph node is a granuloma.
• Granulomas due to infectious agents such as
mycobacteria are often described as "caseating"
when they have prominent caseous necrosis.
• The focal nature of granulomatous inflammation of
lung
• in which there are scattered granulomas in the
parenchyma.
• This is why the chest radiograph with tuberculosis or
other granulomatous diseases is often described as
"reticulonodular".
• A biopsy could miss such lesions from sampling error,
too.
• Giant cells are a "committee" of epithelioid
macrophages.
• Seen here are two Langhans type giant cells in
which the nuclei are lined up around the periphery
of the cell.
• Additional pink epithelioid macrophages
compose most of the rest of the granuloma
• This is a caseating granuloma.
• Epithelioid cells surround a central area
of necrosis that appears
– irregular,
– amorphous, and pink.
• Grossly, areas of caseation appear cheese-like
Granulomas caused by
• tuberculosis and
• pathogenic fungi such as
– Histoplasma capsulatum or Cryptococcus neoformans
• are often caseating.
• Here, the area of caseation is seen at the upper right.
• With a poor immune response to the agents producing
granulomatous inflammation,
• there can be extensive spread of infection
• with the production of a "miliary" pattern of granulomas,
• as seen here in the lung of a patient with miliary
tuberculosis.
• The 1 to 2 mm granulomas are scattered around like millet
seeds (millet is a type of cereal grain).
Types of chronic inflammation
• Granulomatous chronic inflmmation
• Non- granulomatous chronic inflammation
Non- granulomatous chronic inflammation
• Characterized by the accumulation of
– sensitized lymphocytes (activated by antigen)
– Plasma cells
– MP
• In the injured area
• These cells are scattered diffusely throughout the
tissue.
• Do not form granuloma.
• Scattered tissue necrosis and fibrosis are common.
Causes of non- granulomatous chronic
inflammation
1. Characterized by lymphocytes and plasma
cell infiltration of tissues with cell necrosis
and fibrosis
– Chronic viral infection
•
•
Chronic viral hepatitis
Chronic viral infection of CNS
– Autoimmune diseases
•
•
Chronic ulcerative colitis
Hashimoto’s thyroiditis
– Chronic alcoholic liver disease and pancretitis
2. Characterized by diffuse accumulation of MP
with intracytoplasmic microorganisms,
deficient T cell response
– Lepromatous leprosy
– Leishmaniasis
3.Characterized by presence of numerous
eosinophils in conjuction with other
inflammatory cells
– Type I hypersensitivity reactions
•
•
BA
Atopic dermatitis
• Certain etiologic agents such as viruses are more likely to lead to
chronic inflammation,
• as seen here in the lung of a patient with influenza A.
• the inflammatory infiltrates of chronic inflammation are more likely
to be interstitial (within tissues)
• rather than exudative (above surfaces or in spaces) like acute
inflammation.
• You can find both acute and chronic inflammation here.
• This type of mixed inflammation is typical of repeated or
recurrent inflammation.
• Examples
– "acute and chronic cholecystitis" or
– "acute and chronic cervicitis".
• The best possible outcome following an inflammatory process
is complete resolution,
– leaving the tissues intact and undamaged.
• However, chronic inflammation may occur in conjunction with
some degree of scarring.
• Here, chronic inflammation of the bronchi has led to dilation
and scarringwith increased tan to white collagenous tissue.
• Chronic inflammation with destruction of the
bronchial wall is seen here.
• An inflammatory infiltrate extends from the
lumen to the left.
• An abscess may have elements of chronic
inflammation if it persists for some time.
• Thus, it is possible to have a "chronic abscess"
with elements of both acute and chronic
inflammation.
• Seen here in the right middle lung lobe is just
such a chronic abscess.
Healing
Repair
• By formation of granulation tissue
• Contain variety of cells
– Endothelial cells forming blood and lymphatic
vessels
– Myofibroblast (fibroblast )forming collagen
– Astrocytes forming a glial scar in the CNS
– Small round cells- lymphocytes and plasma cells
• Healing of inflammation often involves in growth of
capillaries and fibroblasts.
• This forms granulation tissue.
• Here, an acute myocardial infarction is seen healing.
• There are numerous capillaries, and collagen is being
laid down to form a scar.
• Non-infarcted myocardium is present at the far left.
• These features are all seen in chronic
inflammation
• In chronic suppuration the puss-filled cavity is
lined by acutely inflamed granulation tissue.
– This is the pyogenic membrane
• Vascularity of the granulations predisposes to
haemorrhage
Eg: repeated haemorrhage is frequent in chronic
peptic ulcer
Microscopically,
• this abscess has a mixture of inflammatory cells,
• but the wall of the abscess is "organizing" with ingrowth of capillaries
(filled with red blood cells) and fibroblasts.
• As organization continues there is resolution with decreasing size of the
abscess, until only a scar remains.
•
If the body's defensive systems cannot contain the agent causing the
abscess, then the process may continue and even spread
• The wall of an abscess that is organizing
has granulation tissue, at the left.
• The purulent exudate with some hemorrhage
is seen at the right in the abscess center.
• At high magnification, granulation tissue has
– capillaries,fibroblasts, and a variable amount of
inflammatory cells (mostly mononuclear, but with
the possibility of some PMN's still being present).
• Fibrosis is a salient features of chronic
inflamation
• The resulting cicatrisation leads to many of
the importanat complications of CI
Eg: MS and MR following chronic rheumatic
valvulitis
: Pyloric stenosis chronic gastric ulcer
• The end result of inflammation can be scarring.
• The alveolar walls are thickened and filled with
pink collagen following an autoimmune disease
lasting for decades.
• This is a healing biopsy site on the skin seen a week
following the excision,
• The skin surface has re-epithelialized, and
• below this is granulation tissue with
– small capillaries and fibroblasts forming collagen.
• After a month, just a small collagenous scar will remain.
Effects of chronic inflammation
General effects
• Hyperplasia of mononuclear phagocytic
system
Eg : lymph nodehyperplasia
: hepatomegaly
:spleenomegaly – in chronic malaria, SAIE
:marrow hyperplasia
Systemic immune response
• Antibody production is a feature of most
chronic inflammatory disease
– Demonstration of specific immunogloulins is a
useful diagnostic procedure
• Cell – mediated immune response
– Delayed hypersensitivity reaction
Eg : tuberculin, lepromin, Frei are based upon this.
• Cell- mediated hypersensitivity itself results in
tissue damage.
• Long –continued stress on the antibody
producing mechanism may be associated
amyloid disease.
Changes in the blood
• Anaemia- normochromic, normocytic type.
• Reduction of plasma albumin
• Increase gamma globulin
• Increase ESR
Mechanism Of granuloma formation
• The classic example for the immune
granuloma is that caused by the bacillus of
tuberculosis.
• In this disease, the granuloma is referred to as
a tubercle and
• is classically characterized by the presence of
central caseous necrosis.
• Caseating necrosis is rare in other
granulomatous diseases.
• There are many atypical presentations that
• it is always necessary to identify the specific
etiologic agent by:
– special stains for organisms (acid-fast stains for
tubercle bacilli)
– culture methods (tuberculosis, fungal disease),
– serologic studies (syphilis).
– In sarcoidosis, the etiologic agent is unknown
Granuloma:
bacilli are inhaled by droplets
•
Bacteria are phagocytosed by
alveolar macrophages
•
After amassing substances that
they cannot digest, macrophages
lose their motility, accumulate at
the site of injury and transform
themselves into nodular
collections;
–
•
the Granuloma
A localized inflammatory response
recruits more mononuclear cells
•
The granuloma consists of a
kernel of infected macrophages
surrounded by
–
foamy macrophages and
–
a ring of lymphocytes and
–
a fibrous cuff (containment
phase)
•
Containment usually fails when
the immune status of the patient
changes;
–
the granuloma caseates,
ruptures and spills into the
airway
Pathology of Tuberculosis
Etiology and incidence
Characteristics of mycobacteria
• 2-10micrometer in length.
• Structurally gram positive but also contains large
amount of lipids in the cell wall: making them
acid fast.
• No toxins
• No spores
• Obligate Aerobic
• Elicit granulomatous inflammation.
• M. tuberculosis hominis & M. bovis
• M. avium, M.intracellulare in AIDS - Atypical
TB
• Infects one third of world population..!
• 3 million deaths due to TB every year
• Under privileged population – Crowding, Poverty, malnutrition, economic
burden.
• Since 1985 incidence is increasing in west
– AIDS, Diabetes, Immunosuppressed
patients, Drug resistance.
• Tuberculosis is a chronic communicable
disease in which the lungs are the prime target,
• although any organ may be infected.
•
•
•
•
Primary TB
SecondaryTB
Progressive pulmonary TB
Miliary TB
PATHOGENESIS
• The course of tuberculosis depends on age and
immune competence AND total burden of the
organisms
• Tuberculous Infection: refers to growth of the
organism in a person,whether there is
symptomatic disease or not.
• Active Tuberculosis; refers to infection
manifested by tissue destruction-----symptomatic
disease.
PRIMARY TUBERCULOSIS
• Primary tuberculosis is the form of disease that
develops in a previously unexposed and
unsensitized person.
• Tuberculosis is a type of
– delayed tissue hypersensitivity to the tuberculous
bacillus
– which elicit a cell-mediated immune response
– which will resists the growth and spread of the
mycobacterium.
• This hypersensitivity reaction produces the
pathologic feature of tuberculosis in
immunocompetent individuals,
– i.e. granulomas, caseation, cavity formation
• The sequence of events
– which occur after inhalation of infectious agent in
a previously
•
unexposed immunocompetent individual are:
 The mycobacterium will gain access to the
alveolar macrophage through receptors.
* Once the organisms are inside the
cytoplasm of the macrophage it will inhibit
the microbicidal response of the macrophage
– ineffective phagolysosome
 Multiplication of the organism inside the
alveolar macrophage
processing& presentation of the antigen on the
surface
A clone of sensitized T-cells proliferate, produce
gamma INT.
Activation of the macrophages(augmenting
their capacity to kill mycobacteria)
• The lytic enzymes of the activated
macrophages is released, also damaged host
tissues.
• This activation of macrophages and
destruction of mycobacteria comprises the cell
mediated immunity.
• The earliest stage of primary tuberculosis (<3
weeks) in the nonsensitized individual is
characterized by
– proliferation of bacteria in the pulmonary alveolar
macrophages and airspaces,
– with resulting bacteremia and seeding of multiple
sites
• About 3 weeks after infection, a TH1 response
against M. tuberculosis is mounted that
activates macrophages to become bactericidal.
• TH1 cells are stimulated by mycobacterial
antigens drained to the lymph node.
• Mature TH1 cells, both in lymph nodes and in the
lung, produce IFN-γ.
• IFN-γ is the critical mediator which drives
macrophages to become competent to contain the
M. tuberculosis infection.
• IFN-γ stimulates formation of the
phagolysosome in infected macrophages,
exposing the bacteria to an inhospitable acidic
environment.
• IFN-γ also stimulates
– expression of inducible nitric oxide synthase
(iNOS),
• which produces nitric oxide (NO).
– NO helps in the destruction of several
mycobacterial constituents,
• from cell wall to DNA
• In addition to stimulating macrophages to kill
mycobacteria,
– the TH1 response orchestrates the formation of
granulomas and caseous necrosis.
• Activated macrophages, stimulated by IFN-γ,
produce TNF, which recruits monocytes.
• These monocytes differentiate into the
"epithelioid histiocytes" that characterize the
granulomatous response
• In immunocompromised persons granulomas
are poorly formed or
• not formed at all and
• the infection progress at the primary site in the
– lung
– ,lymph nodes or
– in multiple sites--------progressive primary tuberculosis
PRIMARY TUBERCULOSIS
Is characterized by:
Ghon Focus ----• lung lesion of primary TB,
– involves upper segments of the lower lobes or
– lower seg.of the upper lobe.
Ghon complex----• combination of a peripheral ghon focus and
involved mediastinal or hilar lymphnode.
• Microscopically the classic lesion of TB is a
caseous granuloma
Clinical and pathologic implications of primary
tuberculosis
1] Development of resistance to the infection.
2]
The foci of scarring may harbor viable bacilli
life and act as a nidus for reactivation.
3]
The disease may develop into progressive primary
tuberculosis in immunocompromised patients such as
AIDS patients,
elderly, and
malnourished children.
for
• In patients with progressive primary tuberculosis,
the tissue reaction is different.
• No well-formed granulomatous reaction
caseation necrosis is seen in tissue affected.
or
• Resembles acute bacterial pneumonia with
– lower and middle lobe consolidation,
– pleural effusion and
– hilar lymphadenopathy.
• Cavitary lesions are rare.
• Disseminated disease with tuberculous meningitis
and miliary tuberculosis
• With progressive pulmonary tuberculosis,
– the pleural cavity is invariably involved, and
• serous pleural effusions,
• tuberculous empyema,
• obliterative fibrous pleuritis may develop.
Secondary tuberculosis:
• Is the pattern of disease that arises in a previously
sensitized host.
• Is usually a reactivation of dormant primary lesions when
– the host resistance is lowered.
• Or exogenous reinfection by a high dose of virulent bacilli
which
– occur more commonly in endemic areas.
• Only 5% of patients with primary disease develop
secondary tuberculosis
Pathologic features of secondary tuberculosis:
• In secondary pulmonary tuberculosis, the lesions
involves
– the apices of both lungs and
– appear grossly as sharply circumscribed firm areas
•
with central caseation and cavitation surrounded by fibrous
wall.
• It can heal by fibrosis leaving a residual apical
scar.
• Histologically, epithelioid granulomas with
central caseation and Langhan’s type giant cells.
• Other clinicopathologic forms of secondary
tuberculosis depends on the organ involved
• Includes
– Cough,low grade fever wt.loss, anorxia
– Cavitaton may be accompanied by haemoptysis
• Chest radiographs show unilateral or bilateral
apical cavities.
Complications of secondary TB
• Scarring &calcification
• Spread to other areas
• Pleural fibrosis & adhesions
• Rupture of caseous lesion
• Implantation of bacteria in the larynx --– hoarseness
Miliary tuberculosis
Miliary pulmonary disease
• Occurs when organisms drain through
lymphatics into the lymphatic ducts,
–
–
•
which empty into the venous return to the right side
of the heart and
thence into the pulmonary arteries.
Individual lesions are either
–
–
–
microscopic or small,
visible (2-mm) foci of yellow-white consolidation
scattered through the lung parenchyma.
• Miliary lesions may
– expand and coalesce to yield almost total
consolidation of large regions or
– even whole lobes of the lung.
Miliary tuberculosis is most prominent in :
• the liver,
• bone marrow,
• spleen,
• adrenals,
• meninges,
• kidneys,
• fallopian tubes,
• epididymis
Isolated-organ tuberculosis
• May appear in any of the organs or tissues
seeded hematogenously and
• may be the presenting manifestation of
tuberculosis
• When the vertebrae are affected, the disease is
referred to as
– Pott's disease.
• Paraspinal "cold" abscesses in these patients
may track along the tissue planes to present as
an abdominal or pelvic mass
• Lymphadenitis is the most frequent form of
extrapulmonary tuberculosis,
– usually occurring in the cervical region ("scrofula").
• Intestinal tuberculosis contracted by the
drinking of contaminated milk.
• In developed countries today, intestinal
tuberculosis is more often
– a complication of protracted advanced secondary
tuberculosis,
– secondary to the swallowing of coughed-up infective
material
Diagnosis of TB
• Clinical features are not confirmatory.
• Zeil Nielson Stain - 1x104/ml, 60% sensitivity
• Release of acid-fast bacilli from cavities intermittent.
• 3 negative smears to assure low infectivity*
• Culture most sensitive and specific test.
– Conventional Lowenstein Jensen media 3-6 wks.
– Automated techniques within 9-16 days
• PCR is available, but should only be performed by
experienced laboratories
• PPD for clinical activity / exposure sometime in life.
Special technique for diagnosing
infectious agents
Gram stain
Most bacteria
Acid fast stain
Mycobacteria, nocardiae
(modified)
Silver stains
Fungi, legionellae, pneymocytosis
Period acid-Schiff
Fungi, amebae
Mucicarmine
Cryptococci
Giemsa
Campylobacteria, leishmaniae, malaria,
parasites
Antibody probes
Viruses, rickettsiae
Culture
All classes
DNA probes
Viruses, bacteria, protozoa
Polarizing
microscope
Foreign body
Tuberculin Test
• It is a classic example of delayed
hypersensitivity.
• The tuberculin reaction,
– is produced by the intracutaneous injection of
tuberculin,
• a protein-lipopolysaccharide component of the tubercle
bacillus.
• In a previously sensitized individual,
– reddening and induration of the site appear in 8 to 12
hours,
– reach a peak in 24 to 72 hours, and
– thereafter slowly subside.
Morphologically,
• delayed type hypersensitivity is characterized by
– the accumulation of mononuclear cells around small
veins and venules,
– producing a perivascular "cuffing" .
• Plasma proteins escape,
– giving rise to dermal edema and deposition of fibrin in
the interstitium.
• The latter appears to be the main cause of
induration,
– which is characteristic of delayed hypersensitivity
skin lesions.
• In fully developed lesions,
– the lymphocyte-cuffed venules show marked
endothelial hypertrophy and
– , in some cases, hyperplasia.
Leprosy/Hansen disease
• M. leprae is an acid-fast obligate intracellular
organism that grows very poorly in culture.
• It grows more slowly than other mycobacteria
and grows best at 32° to 34°C, the
temperature of the human skin
• Is a slowly progressive infection caused by
Mycobacterium leprae, affecting the skin and
peripheral nerves and resulting in disabling
deformities.
• M. leprae is likely to be transmitted from
person to person through aerosols from
lesions in the upper respiratory tract.
• Inhaled M. leprae, like M. tuberculosis, is
taken up by alveolar macrophages and
disseminates through the blood, but grows
only in tissues of the skin and extremities.
• leprosy remains endemic among an estimated
10 to 15 million people living in poor tropical
countries
• Like M. tuberculosis, M. leprae secretes no
toxins, and its virulence is based on properties
of its cell wall.
• The cell wall is similar enough to that of M.
tuberculosis.
• Cell-mediated immunity is reflected by
delayed type hypersensitivity reactions to
dermal injections of a bacterial extract called
lepromin
• Leprosy has two strikingly different patterns of
disease.
1)Patients with the less severe form, tuberculoid
leprosy, have dry, scaly skin lesions that lack
sensation. They often have large, asymmetric
peripheral nerve involvement.
• The more severe form of leprosy, lepromatous
leprosy, includes symmetric skin thickening
and nodules. This is also called anergic
leprosy, because of the unresponsiveness
(anergy) of the host immune system
In lepromatous leprosy, damage to the nervous
system comes from widespread invasion of
the mycobacteria into Schwann cells and into
endoneural and perineural macrophages.
- In advanced cases of lepromatous leprosy, M.
leprae is present in sputum and blood.
• People can also have intermediate forms of
disease, called borderline leprosy.
Morphology of Tuberculoid leprosy
• Begins with localized skin lesions that are first
flat and red but enlarge and develop irregular
shapes with indurated, elevated,
hyperpigmented margins and depressed pale
centers (central healing).
• Neuronal involvement dominates tuberculoid
leprosy.
• Nerves become enclosed within
granulomatous inflammatory reactions.
• Nerve degeneration causes skin anesthesias
and skin and muscle atrophy that render the
patient liable to trauma of the affected parts,
with the development of indolent skin ulcers.
• Contractures, paralyses, and autoamputation
of fingers or toes may ensue.
• Facial nerve involvement can lead to paralysis
of the eyelids, with keratitis and corneal
ulcerations.
• On microscopic examination, all sites of
involvement disclose granulomatous lesions
closely resembling those found in
tuberculosis, and bacilli are almost never
found.
• The presence of granulomas and absence of
bacteria reflect strong T-cell immunity.