Human CD56bright and CD56dim natural killer cell subsets respond differentially to direct stimulation with Mycobacterium bovis bacillus Calmette-Guérin

Abstract

Mycobacterium bovis bacillus Calmette-Guérin (BCG) is capable of directly stimulating several effector functions of human natural killer (NK) cells in the absence of interleukin-12 and professional antigen presenting cells. To assess the contribution of two main human NK-cell subsets (CD56 dim and CD56bright) to the overall in vitro NK-cell response to BCG, peripheral blood mononuclear cells depleted of nylon wool-adherent cells or purified NK cells were stimulated with live BCG. By combining intranuclear bromodeoxyuridine (BrdU) staining and analysis of CD56 marker intensity, statistically higher percentages of BrdU+ cells were found among the CD56bright subset than the CD56dim subset after 6 days of stimulation with BCG. Similarly, evaluation of intracellular interferon-γ (IFN-γ) revealed that CD56 bright cells were those mainly involved in IFN-γ production in response to BCG. In contrast, the CD56dim subset contained higher levels of perforin and granzyme A, two key molecules for exocytosis-mediated cytotoxicity, than the CD56bright subset. Although 16-20-h stimulation with BCG did not substantially alter the expression of cytotoxic molecules by die two subsets, a decrease in perforin content was observed in the CD56dim, but not in die CD56bright subset, following 4-h incubation with the NK-sensitive target K562 cell line. This decrease in perforin content correlated with the induction by BCG-stimulated NK cells, of early markers of apoptosis on target cells to a greater extent than unstimulated cells suggesting a major role for the CD56dim subset in cytotoxic activity in response to BCG. Taken together, these results demonstrate that CD56bright and CD56dim human NK-cell subsets exert different functional activities in response to a live bacterial pathogen. © 2005 Blackwell Publishing Ltd.