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Premunition in
Plasmodium falciparum malaria
R. K. Obi1*, C. C. Okangba2, F. C.
Nwanebu1, U. U. Ndubuisi3 and N. M.
Orji4
1Department
of Microbiology, Federal University of Technology, Owerri,
P.M.B. 1526, Owerri, Imo State, Nigeria.
2Department
of Medical Microbiology and Parasitology, College of
Medicine, University Of Lagos, Idiaraba, Lagos, Nigeria.
3Department
of Microbiology, University of Uyo, P.M.B. 1017, Uyo, Akwa
Ibom State, Nigeria.
4Department
of Biological Sciences, Anambra State University, Uli, P. O.
Box 02, Uli, Anambra State, Nigeria.
*Corresponding author. E-mail:
robertobi_2003@yahoo.ca
Accepted 6
January, 2010 |
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Malaria
parasites have evolved to maintain a well-balanced
relationship with their human hosts. This implies that they
can partially escape from protective effector mechanisms of
their hosts, but also that hosts can develop partial
immunity to the parasite. This immunity requires repeated
infections, takes years to develop and is usually of short
duration. However, protective immunity to clinical malaria
rather than infection may be of long duration. This natural
acquired immunity is called premunition since a low
parasitemia mostly persists in the presence of circulating
antibodies to the various stages and in the absence of
clinical disease. In children who do not have circulating
antibodies to the parasite, premunition is probably caused
by antitoxic immunity. These poor and slowly developing
immune responses to malaria are partly due to immune evasion
strategies of the parasite caused by antigenic polymorphism,
shedding of parts of parasite proteins, cross-reactive
epitopes of antigens of different developmental stages,
prolonged exposure to endemic malaria and widespread
restricted immunogenicity to defined antigens.
Premunition
relies on the cooperation between the parasite and human
antibodies, leading to the induction of antibody dependent
cellular inhibition (ADCI) of the intra-erythrocytic growth
of the parasite. The immunity, however, is not a sterilizing
type in that the infection persists longer than the symptoms
and individuals can exhibit relapses or recrudescences or
become reinfected.
Key
words:
Intra-erythrocytic stage, parasitemia, malaria, chronic
stage, human antibodies, immunity. |
