Immunity to protozoa and Helminths

For most of these intracellular infections – the immune response is not efficient enough to eliminate the infection totally – but only achieves this partially. Thus, infection is controlled not eliminated. Innate immunity is useless, so adaptive immunity is of paramount importance.

Protozoans

Antibody acts as an opsonising agent, so that phagocytosis can occur. CD4+ T cells secrete cytokines activating macrophages and B cells. CD8+ T cells differentiate to CTLs and produce cytotoxic T cell effects. Th1 cytokines deal with intracellular parasites whilst TNF-a controls parasitic infection, but can be harmful when produced in large amounts. Granulomas formed to wall off infection – prevent spread.

Helminths

Antibody is very important here, i.e.: IgA inhibits attachment, IgG serves as an opsonin. For tissue parasites, complement fixation via IgA and IgM important (i.e.: they activate complement pathway). IgE causes mast cell degranulation – this increases fluid flow and expulse Helminths from GIT. Eosinophils accumulate at site of infection – mediate ADCC (antigen dependent cellular cytotoxicity).

Category: Pathology Notes