Ex Vivo Interferon-Gamma Immune Response to Thrombospondin-Related Adhesive Protein in Coastal Kenyans: Longevity and Risk of Plasmodium Falciparum Infection

Abstract

Abstract. Thrombospondin-related adhesive protein (TRAP) of Plasmodium falciparum is currently being tested in human vaccine studies. However, its natural reactivity in the field remains poorly characterized. More than 40% of 217 Kenyan donors responded in an ex vivo interferon-␥ (IFN-␥) enzyme-linked immunospot (ELISPOT) assay to at least one of 14 20mer peptides spanning 42% of the antigen. Reactivity was comparable from early childhood (>1 year of age) to old age, and the maximal precursor frequency of TRAP-specific cells to all 14 peptides was 1 in 4,000. Prospective follow-up for one year indicated that these low-level ex vivo responses to TRAP did not protect against the subsequent development of malaria. Retesting of selected donors after one year showed a complete change in the reactivity pattern, suggesting that malaria-specific ex vivo IFN-␥ ELISPOT assay responses are short lived in naturally exposed donors, even to conserved epitopes. This study provides important information regarding natural reactivity to a key malaria antigen.

Gamma Interferon Responses toPlasmodium falciparumLiver-Stage Antigen 1 and Thrombospondin-Related Adhesive Protein and Their Relationship to Age, Transmission Intensity, and Protection against Malaria

“…IFN-␥ responses to LSA-1, for example, were reported to be associated with protection against subsequent infection in children with mild malaria in Gabon (27) but did not correlate with time to infection after drug-induced parasitologic cure of adults and children in Kenya (20,25). Similarly, preexisting IFN-␥ responses to TRAP correlated with higher hemoglobin levels in a prospective examination of Kenyan children (35), whereas there was not a significant relationship between IFN-␥ response and attacks of clinical malaria in children and adults in another area of Kenya (11). The apparently conflicting conclusions of such studies may stem from technical, demographic, and epidemiologic factors.…”

“…The LSA-1 and TRAP 9-mer peptides chosen were predicted to bind to HLA supertypes common in western Kenya (8). The longer LSA-1 (T3) and TRAP (tr51) peptides chosen had elicited strong IFN-␥ responses in other Kenyan populations (11,20). LSA-1 peptides included three 9-mer predicted T-cell epitopes, ls84 (amino acids [aa] 84 to 92; LPMSNVKNV) (3), ls94 (aa 94 to 102; QTNFKSLLR) (15), and ls1881 (aa 1881 to 1889; LFHIFDGDN) (V. Brusic, personal communication), and the 23-mer T-cell epitope T3 (aa 1813 to 1835; NENLDDLDEGIEKSSEELSEEKI) (6,20).…”

“…LSA-1 peptides included three 9-mer predicted T-cell epitopes, ls84 (amino acids [aa] 84 to 92; LPMSNVKNV) (3), ls94 (aa 94 to 102; QTNFKSLLR) (15), and ls1881 (aa 1881 to 1889; LFHIFDGDN) (V. Brusic, personal communication), and the 23-mer T-cell epitope T3 (aa 1813 to 1835; NENLDDLDEGIEKSSEELSEEKI) (6,20). TRAP peptides were the 9-mer tr539 (aa 539 to 547; TPYAGEPAP) (8) and 20-mer tr51 (aa 526 to 545; AGLAYKFVVPGAATPYAGEP) (11). Peptides were synthesized and purified by high-performance liquid chromatography to Ͼ95% purity (Sigma Genosys, St. Louis, Mo.)…”

“…From a technical perspective, the method of assessing IFN-␥ production may be important. Recent studies conducted in The Gambia of responses to TRAP and circumsporozoite protein (CSP) assessed the number of IFN-␥-secreting mononuclear cells by the enzyme-linked immunospot assay (ELISPOT) (10,11,37), while most studies of LSA-1 have measured IFN-␥ production by enzyme-linked immunosorbent assay (ELISA) (20,25,27,35). Interestingly, although an early report suggested an increased sensitivity of the ELISPOT compared to the ELISA for detecting T-cell IFN-␥ responses in persons naturally exposed to malaria (23), there have been to our knowledge no subsequent comparative studies of the two methods for residents of areas where malaria is endemic.…”

Longevity of Genotype-Specific Immune Responses to Plasmodium falciparum Merozoite Surface Protein 1 in Kenyan Children from Regions of Different Malaria Transmission Intensity

“…10 The role of cell-mediated immunity is not as well characterized. Interferon-gamma (IFN-γ) responses appear to be protective against P. falciparum infection but are short lived or fall below the level of detection [11][12][13][14][15] ; however, T cells likely play an important role in control of P. falciparum infections both directly and indirectly via interactions with B cells. 16 MSP1, the most abundant surface protein on P. falciparum merozoites, is a malaria vaccine candidate.…”