Immunity in Medically Important Parasitic Infections: An Overview

Immunity is the rule. It is often incomplete and takes many years to develop and fade away quickly. Immunity is concerned with resistance to infection. Human life is a battlefield in which we are like soldiers attacked from all sides by bacteria, viruses, fungi and parasites. Our body is bestowed with a defence mechanism in the form of an immune system It has long been recognized that infections with parasites, such as intestinal worms, are often accompanied by blood eosinophilia, and this is due to an immunological process. Conditions in which blood eosinophilia is common include intestinal infections with Ancylostoma duodenale, Ascaris lumbricoides, Trichuristrichiura, various forms of Wuchereria bancroft, Brugiamalayi, loaloa, Dracunculus medinensis, mite infection of the lungs (including at least some cases of tropical eosinophilia);and hydrated disease is due to Echinococcus granulosus. Eosinophilia, in large numbers invades tissues in which antigen-antibody reaction has taken place. They appear to be attracted by some product of the antigen-antibody reaction and it has been shown that if tissues from sensitized guinea -pigs mixed with antigen in vitro, or tissues from guinea-pigs which have died from anaphylaxis, are transferred to the peritoneal cavity of normal guinea-pigs, the recipient develops very marked eosinophilia within 24 hours. The active agent has not been infected, but it is probably not histamine. The eosinophils of rodents are very actively phagocytic, and ingest cellular debris, mast cell granules, etc, but it is not certain whether this is true of eosinophils from other species, nor it is known what functions the eosinophils serve in these reactions. A multitude of defensive mechanisms are involved in parasitic infection. A humoral response develops when parasites invade blood stream (Malaria, Trypanosoma), whereas cell-mediated immunity is elicited by parasites that grow within the tissues (Eg: Cutaneous leishmaniasis). Humoral immunity is a function of B cells, memory cells and antibodies. In protozoal infections, IgG, and IgM are produced. In Addition, IgA also produced in intestinal infection. With helminthic infections, IgG, IgM and IgE antibodies are produced.