Human immunodeficiency virus infection and cryptosporidiosis: protective immune responses.

Cryptosporidium parvum is an ubiquitous protozoan parasite that infects the gastrointestinal track, leading to enteritis. The course of the disease is closely linked to the immunocompetence of the host. In patients with human immunodeficiency virus (HIV) infections, the CD4 cell count is the best marker of the ability of the immune system to clear Cryptosporidium infection at the mucosal surface. In HIV seropositive persons who have cleared Cryptosporidium infection, levels of specific anti-Cryptosporidium secretory IgA are elevated compared with persons with acquired immunodeficiency syndrome (AIDS) and chronic cryptosporidiosis. In contrast, anti-Cryptosporidium serum antibody responses are much greater in persons with AIDS and chronic Cryptosporidium infection. Secretory antibody is also effective in neutralizing Cryptosporidium infection in vitro. Secretory IgA may be responsible for recovery from infection or may only be a marker for an effective immune response at the mucosal surface. Specific defeats in secretory antibody responses in patients with AIDS and cryptosporidiosis may be overcome with the development of murine or human monoclonal antibodies for oral immunotherapy.