Cell mediated immunity to Plasmodium vivax infection: in vitro inhibition of parasite growth by monocyte derived macrophages.

ABSTRACT

OBJECTIVE: To study the ability of soluble blood stage or cell associated antigens of Plasmodium vivax to stimulate human peripheral blood mononuclear cells (PBMC) and produce factors capable of causing inhibition of parasite growth in vitro was the objective of this investigation. METHOD: A local isolate of P vivax was either synchronized by triple sorbitol lysis for antigen preparation or used as unsynchronized culture for parasite inhibition, employing a macrophage inhibition assay. The soluble or cell associated antigens of P vivax were added to human monocyte derived macrophages with P vivax parasitized red blood cells. The percent inhibition of parasite growth was examined after 72 hrs by microscopy of Giemsa stained smears of red blood cells from the experimental and control groups. RESULTS: The differences in parasite inhibition were compared using Wilcoxon rank sum test for paired differences. Unstimulated PBMC supernatants did not inhibit parasite growth. Significant inhibition of parasite growth (90%) was seen after incubating P vivax infected erythrocytes with PBMC supernatants resulting from stimulation with soluble antigens (T = 3; P < 0.05). However, the cell associated antigens of P vivax did not stimulate PBMC to activate macrophages for parasite killing in vitro (T = 14, P < 0.05). CONCLUSION: We conclude that the soluble blood stage antigens of P vivax can stimulate human PBMC to produce factors capable of activating macrophages to function as effector cells in P vivax malaria.