Towards A Malaria Vaccine?
The last few years have seen a marked change in the understanding of malaria mmunology.
We have very little knowledge on immunity of Malaria based on experiments in human
beings due to ethical reasons. Whatsoever our knowledge exists at present is based on
experimentas in mice and monkey. However it is clear that it is sporzoite or merozoite
which is directly exposed to our immune system in the life cycle of Malaria parasite. On the
basis of human experiments we can draw inference that immunity to malaria is species.
specific (on cross immunity), stage specific and strain specific as well acquired in the response to surface antigen and relapsed antigen although the parasite also demonstrates escape machanism to immune system.
So the host system kills or elimi nate the parasite by means of (a) Antbody to extracell~
ular form of parasite with the help of mechanism of Block invasion, Agglutination or opsonization and/or (b) Cellular machanism-either by phago-cytosis of parasite or by antibody dependent cellular cytotoxicity ABCC (?) or by effects of mediators like tumor necrosis fJ.ctor (TNF) in cerebaral malaria or crisis forming factor as found in sudan or by possible role of lysis mechanism.
However, inspite of all these theories the parasite has been able to invade the immune
system by virtue of its intracellular development stage specificity, sequestration in capillaries and also by its unusual characteristics of antigenic diversity and antigenic variation.