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IMMUNITY II
DR SATHYA ANANDAM
ACQUIRED IMMUNITY
ACQUIRED IMMUNITY
• Resistance that an individual acquires during life.
• 2 types : Active acquired immunity
Passive acquired immunity
ACTIVE IMMUNITY
• Resistance developed by an individual as a result of an antigenic
stimulus.
• Also called Adaptive immunity.
• Involves active functioning of the host’s immune system leading to
the synthesis of antibodies and / or the production of
immunologically active cells.
• Latent phase, Negative phase, Sec. response,Immunological
memory.
HUMORAL IMMUNITY(ANTIBODY-MEDIATED)
•
Involves production of antibodies against foreign
antigens.
•
•
Antibodies are produced by B cells.
•
Circulating antibodies combines specifically with antigens
and lead to lysis of antigen molecules, or neutralise
toxins, or phagocytosed
B cells that are stimulated will actively secrete antibodies
and are called plasma cells.
CELL MEDIATED IMMUNITY
• Involves specialized set of lymphocytes called T cells that
recognize foreign antigens on the surface of cells, organisms,
or tissues
• T cells regulate proliferation and activity of other cells of the
immune system: B cells, macrophages, neutrophils, etc.
• Defense against:
• Bacteria and viruses that are inside host cells and are
inaccessible to antibodies.
• Fungi, protozoa, and helminths
• Cancer cells
• Transplanted tissue
MECHANISM OF ACQUIRING ACTIVE IMMUNITY.
Contact with Antigen (1st time)
IMMUNE SYSTEM
Contact with SAME
antigen 2nd time
B cells (Plasma cells)
T cell sensitization
Active Antibody
Cytokines
Memory cells
Large number of active antibodies.
Antibody
60
Antibody
40
20
Lag
Antigen
Time
Active Immunity
Time
Passive Immunity
A. Naturally Acquired Active Immunity:
• Obtained through clinical or subclinical infection.
• Antigens or pathogens enter body naturally.
• Body generates an immune response to antigens.
• Immunity may be lifelong (chickenpox or mumps) or temporary (influenza or
intestinal infections) or No immunity against common cold virus infection
• Anti bacterial immunity lasts shorter period
• Premunition: (Infection immunity) Immunity to reinfection lasts as long as
original infection persists (Malaria, Syphilis).
ARTIFICIALLY ACQUIRED ACTIVE IMMUNITY:
• Antigens are introduced in vaccines (immunization).
• Body generates an immune response to antigens.
• Immunity can be lifelong (oral polio vaccine) or temporary (tetanus
toxoid).
VACCINES
Live vaccines
BCG for Tuberculosis
Sabin vaccine for Poliomyelitis
MMR vaccine for Measles,
Mumps, Rubella
17D vaccine for Yellow fever
Killed vaccines
TAB vaccine for enteric fever
Salk vaccine for poliomyelitis

Toxoids
Tetanus toxoid for tetanus
Diphtheria toxoid for
diphtheria
• Subunit vaccines
• Hepatitis B
CHARACTERISTICS OF LIVE AND KILLED VACCINES
Live vaccine:
• Initiates infection without causing injury or disease
• Immunity lasts for several years. Booster doses may be required
• Given intradermally or orally. Oral vaccines produce local immunity or CMI
Killed vaccine:
• Less immunogenic. Booster doses always required
• Immunity lasts for short period
• Given parenteral. Produce AMI
PASSIVE IMMUNITY
• Resistance transmitted to a recipient in a readymade form.
• Preformed antibodies are administered.
• No antigenic stimulus.
• Host’s immune system is not actively involved.
• No latent period or negative phase
• No secondary response
• Acts immediately
NATURALLY ACQUIRED PASSIVE IMMUNITY:
• Antibodies pass from mother to fetus via placenta or breast feeding
(colostrum).
• No immune response to antigens.
• Immunity is usually short-lived (weeks to months).
Artificially Acquired Passive Immunity:
• Preformed antibodies (antiserum) are introduced into body by
injection.
• Immunity is short lived
• Host immune system does not respond to antigens.
ARTIFICIAL PASSIVE IMMUNITY
 Antitetanus
serum (ATS) for tetanus
 Convalescent
sera contain high levels of antibodies. Used for
immunisation of measles and rubella
 Pooled
human gammaglobulin used for immunisation against
Hepatitis A
 Snake
antivenom injection from horses or rabbits.
USES OF PASSIVE IMMUNISATION
i.
To provide immediate short term relief in nonimmunised
individuals
ii. For supression of active immunity which may be injurious
iii. For treatment of serious infections
Active Immunity
Passive Immunity
Produced actively by immune
system
Received passively by the host
Induced by infection or contact with
antigens
Conferred by administration of
readymade antibodies
Long lasting
Short lived
Immunity effective after a lag
period
Immunity immediately effective
Immunological memory present
No immunological memory
Not applicable in immunodeficient
persons
Applicable in immunodeficient
persons
Used for prophylaxis to increase
body resistance
Used to treat acute infections
COMBINED IMMUNIZATION
• Active and Passive immunisation given simultaneously
• ATS + Toxoid : prevent tetanus (Road injury)
• Immunoglobulin + HDCV: Post – exposure prophylaxis (rabies)
ADOPTIVE IMMUNITY
• Injection of immunologically competent lymphocytes
• Transfer factor: An extract obtained from immuno- competent
lymphocytes (Lepr. Leprosy, candidiasis, malignancy, multiple
sclerosis)
LOCAL IMMUNITY
• It is the resistance produced at the local site preventing the entry
and multiplication
• Secretory immunoglobulin (IgA) plays important role preventing
the entry at the primary site.
• Natural infection or live viral vaccine gives local immunity
• Sabin (oral) vaccine (polio) influenza nasal spray
HERD IMMUNITY
• Overall resistance in a community for a specified disease
• Ratio of resistant to susceptible host is important in this immunity.
• It is relevant in control of epidemic diseases (Diphtheria, poliomyetitis etc.)
 When herd immunity is low epidemics occur
 Eradication of disease is dependent on development of herd immunity
HERD IMMUNITY
• Factors influencing:
• Vaccination.
• Quarantine measures.
• Effect of carriers.
• Environment plays major
role.