Immunity in parasitic diseases

Dr. M. FachrizalDepartment of Parasitology

Cells in immune system

Defense mechanism of mucosa to orally infected parasitesNon immunological: - Physical barrier: gut motility, epithelial cell layer - Chemical barrier: gastric acid, pancreatic enzyme, bile, mucusImmunological factors:Gut associated lymphoid tissues (GALT): - lymphoid aggregates in the tonsils - Peyers patch (PPs) in the ileum - mucosal lymphoid follicles - immunological active cells in the laminal propria - lymphocytes scattered between the enterocytes

Immune Response to ParasitesComplexity of parasite structure.

Complexity of parasite metabolism.

Complexity of parasite life cycle.

Existence of migratory phases.

Immune evasion.Is complex Surface antigensInternal antigensExcretory/Secretory antigensShed surface antigens

Innate Immunity to Parasitic Infections1- The skin: forms an important barrier against penetration e.g. Schistosoma and Ancylostoma, W.bancrofti and T.cruzi.

2- Body secretions: - Intestinal secretions wash away luminal parasites e.g. Trichinella spiralis. - Mucus prevents invasion mucosa by helminths and protozoa.

3- Serum factors: high-density lipoproteins (naturally present in serum) may kill parasites as Trypanosoma.

4- Macrophages: attack parasites and destroy them.5- Red cell structure factor:Absence of Duffy antigen: provides resistance to P.vivax infection.

Haemoglobin S: provides resistance to P.falciparum infection. This type of haemoglobin is not suitable for the parasite

Deficiency of G6PD: provides resistance to P.falciparum infection. The parasite needs this enzyme for its development.Duffy antigen

Acquired immunity to Parasitic infectionsWhen a parasite enters the human body an immune response is initiated by antigen presenting cells Th1Th2TCNKMacB cellIL1IL2Cell-mediated immunityHumoral immunityMHC class 2ParasiteAbEosinophils + mast cellsPeptide

Role of T cytotoxic cellsTc cells identify infected cell (target cell) expressing parasite Ag associated with MHC class I. Tc cells release toxic molecules that induce pore formation in cell membrane of infected cell resulting in cell lysis.Release toxic moleculesLysis MHC class1

Role of NK cellsNK cell attacks parasite infected cell directly or by the help of antibody then release toxic products that cause lysis of the target cell.Cell lysisCell lysisEnzymes + toxic granules

Role of Macrophages Antigen presenting cell: Degrading parasite Ag into simple peptides and present them on its surface associated with MHC class 2 molecules.

Intracellular killing of microparasites: Phagocytosing the parasite then killing it inside the phagolysosome.

Extracellular killing of macroparasites: Releasing toxic products onto the parasite.

Role of B cellsDirect killing of parasitePrevent cell invasionInactivation of parasite productsB cells develop into Plasma cells produce Antibodies1- Direct action of antibodiesSecretory IgA

2- Contribution of Ab with other immune elementsIgM and IgG activate complement in the classical pathway leading to cell lysis e.g. red cells infected with malaria parasiteAntibodies coat the parasite making it more easily phagocytosedComplement activationOpsonization Complement activationCell lysis

3- Interaction of antibodies with effector cellsImmunoglobulin molecules act as a link between parasite and effector cells. These cells become activated and release toxic products to digest the parasitemacrophageneutrophilplateleteosinophilMast cellNK cell

Role of Eosinophils Play an essential role against helminthsHigh or moderate eosinophilia: seen with helminths that are invasive and cause inflammation of tissues e.g. Schistosoma and Fasciola.

Little or no eosinophilia: seen with helminths that remain localized to the intestinal tract e.g. Enterobius.

No eosinophilia: seen in infections with protozoa e.g. malaria, amoebiasis, toxoplasmosis, leishmaniasis and trypanosomiasis.

IgGIgERelease mediators

Compare Between MacrophagesAct as antigen presenting cell.

Cause Intracellular killing of microparasites.

Cause Extracellular killing of macroparasites.

EosinophilsPlay an essential role against helminths.

High or moderate eosinophilia: in helminths that are invasive.

Little or no eosinophilia: in helminths that remain localized in the intestinal tract.

No eosinophilia: against Protozoa.

Role of Macrophages and Eosinophils in parasitic infections

Thank You

M.C.Q.Antigen presenting cells initiate immune response by presenting antigen to:a- macrophagesb- eosinophils

Th1 response is directed mainly against:a- Protozoab- Helminths

Duffy antigen present on red cells act as a receptor for:a- Plasmodium falciparumb- Plasmodium malariae

c- T-helper cellsd- Natural killer cellsc- Intestinal protozoad- Intestinal helmithsc- Plamodium vivaxd- Plasmodium ovale