Immune Pathology - Host Response to Infection

IMMUNE PATHOLOGY

The protozoa can elicit humoral responses in which antigen–antibody complexes are formed and these can trigger coagulation and complement systems. Immune complexes have been found circulating in serum and deposited in the kidneys where they may contribute to conditions such as glomerulo-nephritis. In other tissues these complexes can also induce localized hypersensitivities. It is thought that this type of immediate hypersensitivity is responsible for various clinical syndromes including blood hyperviscosity, oedema and hypotension.

Another important form of antibody-mediated pathology is autoimmunity. Auto-antibodies to a number of different host antigens (e.g. red blood cells, laminin, collagen and DNA) have been demonstrated. These auto-antibodies may play a role in the pathology of parasitic diseases by exerting a direct cytotoxic effect on the host cells, e.g. auto-antibodies that coat red blood cells produce haemolytic anaemia; they may also cause damage through a buildup of antigen–antibody complexes.

Many parasites can elicit the symptoms of disease through the action of their surface molecules such as the poreforming proteins of E. histolytica that induce contact-dependent cell lysis, and trypanosome glycoproteins that can fix and activate complement resulting in the production of biologically active and toxic complement fragments. A range of parasite derived enzymes such as proteases and phospholipases can cause cell destruction, inflammatory responses and gross tissue pathology.