Immunological aspects of Giardia infections.

Immunodeficiency, particularly antibody deficiency, predisposes to increased intensity and persistence of Giardia infections. Giardia-infected immunocompetent hosts produce serum and intestinal antibodies against Giardia trophozoites. The number of Giardia muris trophozoites, in mice with G. muris infection, is reduced by intra-duodenal administration of anti-G. muris antibody. Giardia intestinalis antigens that are recognised by human anti-trophozoite antibodies include variable (variant-specific) and invariant proteins. Nitric oxide (NO) appears to contribute to host clearance of Giardia trophozoites. Arginine is a precursor of NO and is metabolised by Giardia trophozoites, possibly reducing its availability for generation of NO by the host. Work with mice suggests that T lymphocytes and interleukin-6 (IL-6) contribute to clearance of Giardia infection via mechanisms independent of antibodies.