Peripheral blood lymphocyte subsets in acute human melioidosis

[Extract] Melioidosis is a gram-negative bacterial infection caused by Burkholderia pseudomallei. Although it often occurs in individuals with coexistent disease predisposing to immunosupression, it also occurs in apparently normal individuals [1]. As it has been shown to be a facultative intracellular pathogen [2], it can therefore evade many of the normal immunological defence mechanisms. However, its pathogenesis remains poorly understood. In human melioidosis clinical studies have demonstrated elevation of TNF-alpha [3], IFN-gamma, IL-2 [4], IL-6, and IL-10 [3] as well as other cytokines and chemokines. Hyperproduction of proinflammatory cytokines is associated with lethality [3]. Studies using a mouse model have (i) shown that eradication of Burkholderia pseudomallei in vitro requires the interaction of cells of the monocyte series with lymphocytes [5], (ii) have demonstrated the absolute dependence of resistance to Burkholderia pseudomallei on IFN-gamma [6], and (iii) shown that NK cells and CD8+ lymphocytes are the sources of this IFN-gamma [7]. In view of these findings, reduction in lymphocyte numbers or function may be important for the survival of this pathogen