Roles of Surface Antigens on Malaria-Infected Red Blood Cells in Evasion of Immunity

Abstract

The life cycle of malaria parasites is extremely complex, involving multiple stages in the invertebrate vector and vertebrate host. However, the clinical manifestations of this disease in humans, and its mortality, are solely attributable to the asexual blood stages of the parasite. Furthermore, the blood stages are the forms of the parasite most susceptible to naturally acquired immunity. This chapter focuses on the surface antigens of infected red blood cells, their potential roles in inducing parasiticidal immune responses upon infection or immunization, their structure when known, and most importantly, recently obtained evidence that some of these surface antigens are involved in different mechanisms for evasion of host-protective immunity. Sections I-IV review the published literature and our own recent results implicating new surface antigens on infected cells as targets of antibody-dependent parasiticidal immune responses. Section V deals with the established capacity of malaria parasites to evade parasiticidal immunity and reviews the range of ways, both theoretical and indicated by experiment, in which this might be achieved Finally, Sections VI and VII describe in detail two mechanisms for parasite evasion of immunity, with emphasis on recent experimental results from this laboratory. It is beyond the scope of this chapter to review mechanisms of malarial immunity not involving new antigens on infected erythrocytes. Excellent descriptions of alternative mechanisms are given elsewhere(K.N. Brown, 1976; Cohen, 1979; Kreier and Green, 1980; McGregor, 1981; Allison, 1981; Jayawardena, 1981).