Antigenic polymorphism in malaria: is it an important mechanism for immune evasion?
✍ Scribed by Kamini N. Mendis; Peter H. David; Richard Carter
- Publisher
- Elsevier Science
- Year
- 1991
- Tongue
- English
- Weight
- 494 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0167-5699
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✦ Synopsis
Malarial infections do not readily evoke an effective protective immunity against re-infection. Possible reasons for this include the ability of the parasites to interfere with the host's immune response and to evade the response in an immune host, by, for example, exploiting antigenic polymorphism or variation. Antigenic polymorphism undoubtedly exists in malaria parasite populations but does this polymorphism actually contribute to immune evasion by the parasite? Here, Kamini Mendis and colleagues examine the evidence for this and its implications for future malaria vaccines.
Malaria evokes a poor protective immunity in humans.
Residents of endemic areas suffer repeated infections and, after several years of exposure to intense malaria transmission, acquire a partially protective immunity; this is a nonsterile immunity, which leads at best to a state of premunition in which low parasite densities prevail in the host without causing acute disease'. Despite the slow acquisition of protective immunity, early observations on malaria infections therapeutically induced in neurosyphilitic patients showed that individuals convalescing from Plasmodium viuax infections acquire a potent immunity to the strain of the parasite that caused the infection but not to a heterologous strain2. These observations imply that an effective host immunity is in fact mounted against the homologous parasite but that this immunity is strain specific. The slow acquisition of immunity to natural malaria infections may, therefore, be partly due to the existence of immunological differences between parasite inocula that are prevalent in nature. This view is in accordance with the existence of antigenic polymorphism among malaria parasites in natural popu-lations3*4. In this review, evidence relevant to the possible significance of parasite antigenic polymorphism to immune evasion by the parasite and to the acquisition of immunity by the human host is examined.