Changes

The first line of defence against parasitic infection are the effector mechanisms of the innate immune system:

*'''Macrophages'''- important in the defence against extracellular parasites, macrophages are able to secrete cytokines as well as perform phagocytosis

The first line of defence against parasitic infection are the effector mechanisms of the innate immune system.

**Can act as 'killer cells' through antibody-dependent cell-mediated cytotoxicity, e.g. specific [[IgG]]/[[IgE]] enhances the ability of macrophages to kill schistosomules

 

The '''[[Macrophages|Macrophages]]''' are important in the defence against extracellular parasites. This is because macrophages are able to secrete cytokines as well as perform phagocytosis. In this they can act as 'killer cells' through antibody-dependent cell-mediated cytotoxicity, for example specific [[Immunoglobulins|IgG]]/[[Immunoglobulins|IgE]] enhances the ability of macrophages to kill schistosomules through the interaction of Fc receptors on the surface of the macrophage.

**The secretion of TNF-alpha:

**The secretion of TNF-alpha:

***Activates other macrophages

***Activates other macrophages

**Like other effector cells, platelets express Fc receptors, making them able to perform antibody-dependent cytotoxicity

**Like other effector cells, platelets express Fc receptors, making them able to perform antibody-dependent cytotoxicity

Although the innate immune system provides an effective first line of defence, T cells are fundamental in the development of immunity, demonstrated using T-cell deprived mice that fail to resolve otherwise non-lethal infections of, for example, ''T. cruzi''.  

Although the innate immune system provides an effective first line of defence, T cells are fundamental in the development of immunity, demonstrated using T-cell deprived mice that fail to resolve otherwise non-lethal infections of, for example, ''T. cruzi''.  

*Both CD4+ and CD8+ cells are required for protection, e.g CD4+ cells protect against the blood stage of a Plasmodium infection (erythrocytes do not express MHC class I), while CD8+ cells are required to mediate immunity against the liver stage (hepatocytes do not express MHC class II).

*Both CD4+ and CD8+ cells are required for protection, e.g CD4+ cells protect against the blood stage of a Plasmodium infection (erythrocytes do not express MHC class I), while CD8+ cells are required to mediate immunity against the liver stage (hepatocytes do not express MHC class II).

*Involvement in antibody-dependent cell-mediated cytotoxicity

*Involvement in antibody-dependent cell-mediated cytotoxicity

'''Immunopathology'''

=='''Immunopathology'''==

*The increase in macrophages and lymphocytes in the liver and spleen can lead to swelling of these organs, e.g. visceral leishmaniasis

*The increase in macrophages and lymphocytes in the liver and spleen can lead to swelling of these organs, e.g. visceral leishmaniasis

*T-cell dependent granulomas forming in organs, e.g. schistosomiasis in the liver

*T-cell dependent granulomas forming in organs, e.g. schistosomiasis in the liver

*Excessive production of cytokines, such as TNF-alpha, may contribute to pathology of diseases such as malaria

*Excessive production of cytokines, such as TNF-alpha, may contribute to pathology of diseases such as malaria

'''Evading immune defences''':

=='''Evading immune defences'''==

Parasites can evade an immune response from the host by changing the antigens presented to the host, produce antigens that mimic the host's antigens and can produce down-regulating factors which suppress or modify the host's immune responses. Having a rapid turnover of their surface coat when host cells bind and by being able to live in sites which are protected from the host's immune response allow parasites to establish themselves in a particular species.

Parasites can evade an immune response from the host by changing the antigens presented to the host, produce antigens that mimic the host's antigens and can produce down-regulating factors which suppress or modify the host's immune responses. Having a rapid turnover of their surface coat when host cells bind and by being able to live in sites which are protected from the host's immune response allow parasites to establish themselves in a particular species.