Download Symptomatic HIV Infection

Human Immunodeficiency Virus
&
AIDS
lecture 4
29/9/2010
*In this lecture the dr. will discuss the last virus that causes blood stream infection,
which is HIV
*It belongs to the retroviridae family, It has a reverse transcriptase enzyme, which is
an essential retroviral enzyme that copy a DNA strand from an RNA template
strand
*It is roughly spherical with a conical core that is made of a capsid (P24)
*It is enveloped with about 72 surface glycoproteins, each one is made of 2 subunits :
1) transmembrane subunit called gp41
2)viral attachment peptide subunitcalled gp120
--both are synthesized from the glycoprotein precursor gp160(the envelope of the
virus)-*The virus attach to the cell via gp120
*It has matrix protein that link the core to the envelope (p70),capsid (p24) &
additional proteins associated with the genome for its organization
*All retroviruses have 3 main genes: 1)GAG-group antigen2)POL-polymerase3)ENV-envelope*The virus has 2 identical copies of RNA strand associated with reverse transcriptase
*When the virus get access to the susceptible cell,in the cytoplasm it start copying ssRNA
to ssDNA ,then RNA is digested by RNAase & a complementary DNA strand is
synthesized
known as provirus
*This provirus migrate to the nucleus where it circulated & become integrated in the
genome( it may start replication or remain integrated in the genome )
HIV particles
HIV half-lives
#Activated cells that become infected with HIV produce virus immediately and die within one to two
days.
#Production of virus by short-lived activated cells(source of viremia) accounts for the vast majority
of virus present in the plasma.
*during HIV infection the virus presents in high concentration & the source of this
viremia is the recently infected cells;we have both types of viremia;cell associated
viremia & plasma free viremia.
#The time required to complete a single HIV life-cycle is approximately 1.5 days.
#Resting cells(long lived cells) that become infected produce virus only after immune stimulation;
these cells have a half-life of at least 5-6 months.
*replication of viruses will result in a defective viruses, they have structures that enable
them to establish infection, so they may infect cells & such cells are very long lived.
#Some cells are infected with defective virus that cannot complete the virus life-cycle. Such cells are
very long lived, and have an estimated half-life of approximately three to six months.
*these long lived cells whether resting or those with detectable viremia, are major
challenge for anti viral therapy because the virus is in accessible & antiretroviral
therapy doesn’t affect such cells..
#Such long-lived cell populations present a major challenge for anti-retroviral therapy
In short lived cell 1.5d,minutes in plasma,5-6 months in
long lived cells& 3-6 months if it’s defective…
Antigenic Variation (imp.
Feature of HIV)
#The reverse transcriptase is very error prone and lacks proof reading which contribute to
HIV diversity.
*frequency of errors are very high as compare to other viruses about 5 errors during
copying of 1000 nucleotide which leads to structural changes that lead to inability
of the immune sys. To eleminate them..
#The immune response of the host is unable to completely curtail viral replication(because
of the structural changes).
#Virus gene products may be relatively invisible to the immune response and the virus may
be able to mask or change its antigenic specificity.
#The env. gene displays frequent mutations.
*neutralization of infectivity is the result of AB produced against gp120 & these
structures keep changing_____so the produced AB may not recognise the new vaient(it
need more time )
#HIV envelope glycoproteins have two unusual features.
- They are extensively glycosylated
- They contain hypervariable regions that permit the virus to present to the host new
antigenic configurations.
*both factors impede immunity against HIV
------So it’s not a true single infection(similar to hepatitis C virus)------
#HIV can constantly vary its surface antigenic composition which may allow it to avoid
inactivation.
#Such a mechanism hinders the development of an effective vaccine containing the surface
glycoproteins.
#Major sequence differences exist between the two HIV types; antibodies against the
surface glycoprotein of HIV type 1(most common one) only partially cross react with
HIV type 2.
*AB produced against HIV1 doesn’t neutralize against HIV2 because there is a difference
in their structures
Pathogenesis
#Major targets of HIV-1 are the lymphoreticular, hematopoietic, and nervous systems.
#Critical target cells are dendritic cells,langerhans cells,microglial cells, CD4+ cells and
monocyte -macrophages.
#The CD4 receptor appears to be the principal receptor for both HIV-1 and HIV-2.
#A second receptor, a chemokine receptor (CX CR4 or CC-CKR5) is also required(cuz CD4+
cells are not sufficient alone)
*individuals who lack chemokine receptor are naturally resistant to HIV infection
Early Phase HIV Infection
#In early phase HIV infection, initial
viruses are Macrophage-tropic.
Their envelope glycoprotein gp120 is
able to bind to CD4 molecules and
chemokine receptors called CCR5
found on macrophages
Late Phase HIV Infection
#In late phase HIV infection, most of the
viruses are T lymphocyte -tropic,
having gp120 capable of binding to
CD4 and CXCR4 found on T4lymphocytes.
#Cell killing takes place by different mechanisms.
*during replicative cycle of HIV ,the infected cell die because some of the proviral DNAs
don’t integrate with the genome & that leads to change in the membrane
permeability
multinucleated giant cells formation(gp41 is a fusing agent)
Immune attake
cell killing
#Macrophage-tropic Vs T-lymphocyte-tropic isolates.
#During primary infection, high levels of plasma and cell associated viremia occur.
#Almost all the virus present in an individual’s circulation is the product of recently infected
cells(macrophage or T-lymphocyte).
*latently infected cells don’t contribute in the viremia
#Virus is readily detectable(can be isolated) in peripheral blood and lymph nodes
throughout the course of infection.
*the virus is released from the infected cell
immune sys. Acts to contain viral
infection through activation of CD8+ T cells for killing viral infected cells & through
activation of CD4+Tcells to produce AB.
*both act to eliminate the v. from the circulation
viral entrapping within follicular
dendritic cells
at the same time more cells are infected
more viruses are
produced
the capacity of the individuals to prduce more CD4 & macrophage is
paralyzed
progression of the disease.
*so high viral titers in the blood is associated with recruitment of large no. Of Tlymphocyte,109 CD4 cells are produced daily & the virus is released in the same no.
#Fatal disease occurs because the virus outpaces the immune system and causes
progressive depletion of CD4+ T cells
#High turnover of virus and CD4+ lymphocytes.
#Disease progression appears related to degeneration of the follicular dendritic
network and loss of the HIV-trapping capacity.
#Virus load at any point of time is an important determinant.
*at any point of time HIV can be isolated from infected individuals
*virus load is the most imp. Quantitative indicator especially after the acute phase.
#The best quantitative indicator of future disease is the level of virus that persists in the
blood plasma once the symptoms of acute viremia have passed.
*virus load determine the out come of the disease so it is a prognostic factor
viral load associated with rapid progression & short survival time of individuals
(vice versa)
high
#Over 95% of HIV infected individuals progress to AIDS within 15 years of infection.
*the time required for progressing to full prone AIDS not asymptomatic or latent period
is 2 yrs, but there are causes without any treatment remain latent for 20yrs
*antiretroviral therapy aims to prolong the latent period (the v. is untreatable), so the
target for the therapy is the asymptomatic period that followed the primary infection.
#AIDS is a constellation of clinical illnesses, primarily opportunistic infections and
malignancies.(not just a single illness, it involves diff. systems)
# Manifestations can be attributed to the loss of the functions of the CD4+ T lymphocytes.
*CD4 is imp to mount cell mediated & humeral imm response as well as for phagocytosis
so loss of its function results in manifestation of AIDS
#The CD4+ T cell count in peripheral blood is used as the most important basis for staging
of the disease.
*CD4 isn’t useful for prognosis but it’s imp for staging
#Neuropathogenesis is obscure.
*one of the targets of the virus is CNS(involved in 60% of cases) leads to brain atrophy,
poliosis of the cortex,, perivascular inflammation & white matter degeneration.
* CNS is involved in 60% of cases, leads to manifestation in primary infection ,it’s
commonly involved in the form of meningitis,meningioencephalitis, psychotic
changes as depression, in the late coarse of the disease (
lymphoma,+malignancy+dementia-charecteristic feature of full prone AIDS-) are
developed
#Many factors affect survival rates.
#Specific anti-HIV antibodies generally appear within 6-12 weeks after infection.
(but they may be delayed for up to 6 months, named as window period(no AB can be
detected)
#infected individuals develop both humoral and cell-mediated responses against the virus.
*both are efficient but they can't cope with the ability of structural changing of the
virus
#Mothers who are newly infected and breast feed their infants transmit HIV
40% of the time, showing that HIV can also be transmitted in breast milk.
•
#Between 15% and 30% of children born to untreated HIV-infected mothers
acquire infection.
•
#Recent studies have shown that this rate can be reduced to ~5% when HIV
infected pregnant women receive antiviral drugs.
•
Clinical Features divided into 3 stages:
Acute primary Infection Syndrome(=retroviral syndrome)
(clinical category A)
Asymptomatic Infection and Persistent Generalized Lymphadenopathy (PGL/ clinical category
A)
Symptomatic HIV Infection (clinical categories B and C)
*clinical categories (A,B,C) are based on CD4+Tcell count:
if CD4 is more than 500
A
if CD4 is between 200 & 499
B
if CD4 is between 0 & 199
C
Primary HIV Syndrome
(after incubation period of few days to 3 months & the
incubation period can varies depending on the route of infection;IV blood abuse ,blood transfusion,
neonatal spread or sexual contact)
#Mononucleosis-like, cold or flu-like symptoms may occur 6 to 12 weeks after infection.
-Lymphadenopathy
-fever
-rash
-headache
-Fatigue
-diarrhea
-sore throat
-neurologic manifestations.
-no symptoms may be present
*they may involve any system & patient rarely seek medical care centers that’s why
the virus gone unnoticed ,HIV isn’t suspected in the primary syndrome &
sometimes there is no symptoms at all.
* In this phase patients are (-)ve for HIV Abs, but they may differ according to the
incubation period.
Primary HIV Syndrome
#Symptoms are relatively nonspecific.
#HIV antibody test often negative but seroconversion takes place within 3 to 6 months.
#Large amount of HIV in the peripheral blood. (patients are highly infectious)
#Primary HIV can be diagnosed using viral load titer assay or other tests.
#Primary HIV syndrome resolves itself and HIV infected person remains asymptomatic for a
prolonged period of time, often years. (which is the clinical latency period)
Clinical Latency Period
#HIV continues to reproduce, CD4 count gradually declines from its normal value of 5001200.
#Once CD4 count drops below 500, HIV infected person is at risk for opportunistic
infections.
#The following diseases are predictive of the progression to AIDS:
-persistent herpes-zoster infection (shingles)
-oral candidiasis (thrush)
-oral hairy leukoplakia
-Kaposi’s sarcoma (KS)
*patients with any of these symptoms should be investigated for possible HIV infection ,of
course in the presence of risk factors(IV drug abuse, mother with HIV infection.
Homosexually persons, blood transfusion)
----------------At any point of time viral replication takes place-----------------
Oral Hairy Leukoplakia
#Being that HIV reduces immunologic activity, the intraoral environment is a
prime target for chronic secondary infections and inflammatory processes,
including OHL, which is due to the Epstein-Barr virus under
immunosuppressed conditions
Kaposi’s sarcoma (KS)
#Kaposi’s sarcoma is a rare cancer of the
blood vessels that is associated with
HIV. It manifests as bluish-red ovalshaped patches that may eventually
become thickened. Lesions may appear
singly or in clusters.
*it affects both skin & mucus
membrane.
AIDS (the last symptomatic phase)
#When CD4 count drops below 200 the person is considered to have advanced HIV disease
#If preventive medications not started, the HIV infected person is now at risk for:
-Pneumocystis carinii pneumonia (PCP)(it’s the presenting symptom when AIDS was
discovered in 1978 along with Kaposi’s sarcoma)
-Cryptococcus meningitis
-Toxoplasmosis (can affect the brain & other tissues)
#If CD4 count drops below 50:
-Mycobacterium avium intracellulare complex
-Cytomegalovirus infections
-lymphoma
-dementia
-Most deaths occur with CD4 counts below 50
*****The presenting symptom is PCP*****
Other Opportunistic Infections
#Respiratory system
#Central/peripheral Nervous system
-Pneumocystis Carinii Pneumonia
(PCP)
-Tuberculosis (TB)
-Kaposi's Sarcoma (KS)
-Cytomegolavirus
-Toxoplasmosis
-Cryptococcosis
-Non Hodgkin's lymphoma
-Varicella Zoster
-Herpes simplex
#Gastro-intestinal system
-Cryptosporidiosis (severe diarrhea)
-Candida
-Cytomegolavirus (CMV)
-Isosporiasis
-Kaposi's Sarcoma
#Skin
-Herpes simple
-Kaposi's sarcoma
-Varicella Zoster
Infants with HIVhave different manifestation:
#Failure to thrive
#Persistent oral candidiasis
#Hepatosplenomegaly
#Lymphadenopathy
#Recurrent diarrhea
#Recurrent bacterial infections
#Abnormal neurologic findings.
*It’s easy to diagnose neonates because of their history with the disease.
Immunologic Manifestations
#Early stage slight depression of CD4 count, few symptoms, temporary.
#Window of up to 6 weeks before antibody is detected, by 6 months 95% positive.
#During window p24 antigen present, acute viremia and antigenemia (characteristic of
window period+ end stage priod) (testing for Abs is –ve during this period).
#Antibodies produced to all major antigens.
-First antibodies detected produced against gag proteins p24 and p55.
-Followed by antibody to p120 and gp41 (diagnostic assays utilize ABs for gp41 &
gp120)
-As disease progresses antibody levels decrease.
Immunologic Manifestations
#Immune abnormalities associated with increased viral replication.
-Decrease in CD4 cells due to virus budding from cells, fusion of uninfected cells with
virally infected cells and apoptosis.
-B cells have decreased response to antigens possibly due to blockage of T cell/B cell
interaction by binding of viral proteins to CD4 site.
-CD8 cells initially increase and may remain elevated.
-As HIV infection progresses, CD4 T cells drop resulting in Immunosuppression and
susceptibility of patient to opportunistic infections.
-Death comes due to immune-incompetence.
*there is an inverted ratio between CD8 & CD4 , CD8 are more than CD4
#AIDS Related Dementia is observed in (25-66)% of individuals (leads to
intellectual decline),they may develop many manifestation that are similar to the
manifestations seen in the early phase of Alzheimer disease)
#Markers of Progression to AIDS
- Increased viral load (most imp prognostic factor)
- P24 antigenemia (start in the early infection & it’s also a mark for late end stage
infection)
- Decline of anti P24 antibodies also it’s the first AB to be produced
- CD4+ T cell count below 200 cells/mm3
‘typical’ primary HIV-1 infection
symptoms
symptoms
HIV proviral DNA
HIV antibodies
‘window’
period
HIV viral load
HIV-1 p24 antigen
0
1
1° infection
2
3
4
5
6
/
2
4
weeks
6
8
years
Time following infection
10
*Window period starts early up to 3 months,
characterized by lacking of all markers & no Abs
being produced (no symptoms are observed).
*HIV-p24 antigenemia & HIV viral load increase at the
end of the disease.
Laboratory Diagnosis of HIV Infection
#Methods utilized to detect:
-Antibody
-Antigen
-Viral nucleic acid
-Virus in culture
*CD4 test isn’t a specific diagnose for HIV
Laboratory Diagnosis
#Serology is the usual method for diagnosing HIV infection.
#Serological tests can be divided into screening and confirmatory assays.
*screening test is used first to establish the diagnosis & it should be very sensitive , it
aims to detect as many as possible of those infected (that’s why blood is screened by
very sensitive methods), specifity isn’t imp
#Screening assays should be as sensitive whereas confirmatory assays should be as
specific as possible.
#Screening assays
-ELIAs are the most frequently used screening assays.
-The sensitivity and specificity of the presently available commercial systems now
approaches 100% but false positive and negative reactions occur.
-Some assays have problems in detecting HIV-1 subtype O.
*if the individual is reactive for ELISA , we do the confirmatory test
ELISA for HIV antibody
Microplate ELISA for HIV antibody: colored wells indicate reactivity
*yellow wells contain reactive (serum or syrup -I couldn’t hear it well,sry-) &
there’s Ph indicator
*Ph change will result in the development of colorful reactive specimens, they are
very easy to be interpreted by special machine (it can give a cut of value above it
(+),below it (-)
#Confirmatory assays
-Western blot is regarded as the gold standard for serological diagnosis.
-However, its sensitivity is lower than screening EIAs.
-Line immunoassays incorporate various HIV antigens on nitrocellulose strips.
-The interpretation of results is similar to Western blot. It is more sensitive and specific.
Western Blot
#Most popular confirmatory test.
-Utilizes a lysate prepared from HIV virus.
-The lysate is electrophoresed to separate out the HIV proteins (antigens).
-The paper is cut into strips and reacted with test sera.
-After incubation and washing anti-antibody tagged with radioisotope or
enzyme is added.
-Specific bands form where antibody has reacted with different antigens.
-Most critical reagent of test is purest quality HIV antigen.
-The following antigens must be present: p17, p24, p31, gp41, p51, p55, p66,
gp120 and gp160.(large no. of AGs should be used.
Western Blot
#Antibodies to p24 and p55 appear earliest but decrease or become undetectable.
#Antibodies to gp31, gp41, gp 120, and gp160 appear later but are present
throughout all stages of the disease.
#Interpretation of results.
-No bands, negative.
-In order to be interpreted as positive a minimum of 3 bands directed against
the following antigens must be present: p24, p31, gp41 or gp120/160.
#CDC criteria require 2 bands of the following: p24, gp41 or gp120/160.
Western blot for HIV antibody
#There are different criteria for the
interpretation of HIV Western blot
results e.g. CDC, WHO, American
Red Cross.
#The most important antibodies are
those against the envelope
glycoproteins gp120, gp160, and
gp41
#p24 antibody is usually present but
may be absent in the later stages of
HIV infection
* A minimum 2 bands or 3 bands in other
health authority should be (+)ve
Other diagnostic assays
molecular methods are commonly utilized
#It normally takes 4-6 weeks before HIV-antibody appears following exposure.
#A diagnosis of HIV infection may be made earlier by the detection of HIV antigen, proDNA, and RNA.
#However, there are very few circumstances when this is justified e.g. diagnosis of HIV
infection in babies born to HIV-infected mothers.
Prognostic tests
#Once a diagnosis of HIV infection had been made, it is
important to monitor the patient regularly for signs of
disease progression and response to antiviral chemotherapy.
# HIV Antigen tests
- They were widely used as prognostic assays.
-It was soon apparent that detection of HIV p24 antigen was
not as good as serial CD4 counts.
-The use of HIV p24 antigen assays for prognosis has now
been superseded by HIV-RNA assays.
#HIV Viral Load
- HIV viral load in serum may be measured by assays which detect HIVRNA e.g. RT(reverse transcriptase)-PCR, NASBA(nucleic acid sequence
based amplification), or bDNA(branched).
-HIV viral load has now been established as having good prognostic
value, and in monitoring response to antiviral chemotherapy.
….