The percentage of peripheral blood mononuclear cells (PBMC) bearing the CD3+ phenotype and the alpha/beta and gamma/delta T cell receptors (TCR) in PBMC were examined in Plasmodium vivax malaria patients and convalescents. The cells were labeled with monoclonal antibodies, stained with either fluorescence or phycoerythrin, and examined by ultraviolet (UV) microscopy. A highly significant increase in both the proportion and the absolute numbers of gamma/delta T cells (p < 0.005 and < 0.001, respectively, Student's t test) was observed in nonimmune P. vivax patients during clinical paroxysms compared to nonmalarial controls. These T cells, which normally constitute not more than 3-5% of PBMC, constituted < or = to 30% of PBMC during paroxysms in these nonimmune patients in whom the clinical symptoms were severe. A less significant increase of gamma/delta T cells were also observed in these nonimmune patients during infection, between paroxysms and during convalescence. In contrast, in an age-matched group of semi-immune patients resident in a malaria-endemic region of the country, in whom the clinical disease was comparatively mild, there was no increase in gamma/delta T cells either during infection, even during paroxysms, or convalescence. The severity of disease symptoms in patients as measured by a clinical score correlated positively with the proportion of gamma/delta T cells in peripheral blood (r = 0.53, p < 0.01), the most significant correlation being found between the prevalence and severity of gastrointestinal symptoms, nausea, anorexia, and vomiting, and the proportion of gamma/delta T cells (r = 0.49, p = 0.002). These findings suggest that gamma/delta T cells have a role to play in the pathogenesis of malaria, possibly in the general constitutional disturbances and particularly in gastrointestinal pathology in malaria.

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