There are two main types of immunity against parasitic infections: innate and acquired. The innate immune system provides initial defenses through barriers like skin and secretions, as well as cells like macrophages. Acquired immunity develops through antibody production by B cells and cellular responses by T cells. However, parasites have evolved strategies to evade the immune system, such as living intracellularly, antigenic variation, immunosuppression, migration, and producing enzymes. This makes the immune response less effective against parasites compared to other pathogens.

2.  Like other infectious agents,parasites also induces
immune resistance in its host.
 Immunological protection against parasitic infection
is much less efficient.

3.  Malaria - Plasmodium vivax
 Amoebiasis - Entamoeba histolytica
 Leishmaniasis - Leishmania

4. There are two main types types of immunity:
 Innate
 Acquired

5.  SKIN:
Forms an important barrier of penetration.
eg: W.bancrofti
 BODY SECRETIONS:
Intestinal secretions wash away luminal parasites
eg: Trichinella spiralis
 MACROPHAGES:
Attack parasites and destroy them
 RED CELL STRUCTURE:
 HbS provide resistance to P.falciparum
 G-6PD deficient people provide resistance to
P.falciparum

6.  Antibody response
 Cellular response

7.  Specific immune responses to parsites results in
antibody production.
 Produced by plasma cells
 Mainly IgG and IgM
 Helminthic infection-IgE

8.  NEUTRALISATION :
 Antibody combines with surface molecule of
parasite and neutaralise them.
 Block attachment to host cells
 Antibody binds to toxins and enzymes of parasites,
thus protecting host.
 AGGLUTINATION:
 Agglutination of blood parasite by IgM antibody
 Prevents spread of parasite
 Eg trypanosoma cruzi

9.  OPSONISATION:
 Antibody can act as opsonin and enhances clearances
by phagocytes
 eg.protozoa
 PHYSICAL CLEARANCE :
 Block orifices of certain worms and can cause
starvation or curtail reproduction.
 ANTIBODY DEPENDENT CYTOTOXICITY:
 Complement mediated cell lysis
 Effector cells,macrophages,monocytes , neutrophils
and eosinophils combine with Fc and complement
receptors of antibody coated parasites.

10.  T-LYMPHOCYTES:
 CD 4+T cells act as helper cells in antibody
production
 CD+8 cells are cytotoxic
 MACROPHAGES:
 Play dominant role in process of elimination of
protozoa or worms
 GRANULOCYTES:
 Neutrophils and eosinophils play important role in
elimination of protozoa and helminthes

11. THE PATHWAY OF SPECIFIC IMMUNE RESPONSE
Step 1
Pathogens eaten by Macrophage
Step 2
Displays portion of Pathogen
on surface
Step 3
Pathogens
Helper-T cell recognizes
Pathogen

12. Activates Cytotoxic Activates B- Cell
T- Cell
Memory B-Cell
Memory T-Cell
Antibodies
Kills Infected Cells

13. IMMUNE RESPONSE SUMMARY
Antigen
Displays copy of antigen
on surface of cell
Macrophage
Helper T - Cell
Cellular Antibody Immunity
Immunity
Active Cytotoxic T-Cell Active B - Cell
Kills Infected Cells Memory T- Cell Plasma Cell Memory B-Cell
Antibodies
Deactivates Antigens

14.  Complexity of parasitic structure.
 Complexity of parasitic life cycle
 Immune evasion
 Larger size of parasites
 Intracellular location of many protozoa

15.  Successful parasites have evolved
strategies for survival & development

16.  INTRACELLULAR HABITAT:
 Parasites may live intracellularly. By replicating
inside host cell parasites avoid immune response.
 Plasmodium lives inside Red Blood Cells (RBC’S)
which have no nucleus, when infected not
recognised by CTL’s & NK cells. Other stages of
Plasmodium live inside liver cells.

17.  ANTIGENIC VARIATIONS:
 In Plasmodium, different stages of the life cycle
express different antigens. We will describe evasion
strategies of Plasmodium in more detail in the next
lecture.
 Antigenic variation also occurs in the extracellular
protozoan, Giardia lamblia.
 ANTI-IMMUNE MECHANISMS:
 Leishmania produce anti-oxidases to counter
products of macrophage oxidative burst

18.  IMMUNOSUPPRESSION:
 manipulation of the immune response. High
burdens of nematode infection often carried with
no outward sign of infection.
 Growing evidence that parasite secreted products
include anti-inflammatory agents which act to
suppress the recruitment and activation of effector
leukocytes.
 E.g. a hookworm protein which binds the ß
integrin CR3 & inhibits neutrophil extravasation.

19.  MIGRATION:
 Hookworms, move about gut avoiding local
inflammatory reactions.
 PRODUCTION OF ENZYMES:
 Filarial parasites secrete a number of anti-oxidant
enzymes such as glutathione peroxidase &
superoxide dismutase which most likely contribute
to their observed resistance to antibody-dependent
cellular cytotoxicity and oxidative stress.