Functional characterization of human natural killer cells responding to Mycobacterium bovis bacille Calmette‐Guérin

Abstract

SUMMARYThe kinetics of activation and induction of several effector functions of human natural killer (NK) cells in response to Mycobacterium bovis bacille Calmette-Gue´rin (BCG) were investigated. Owing to the central role of monocytes/macrophages (MM) in the initiation and maintenance of the immune response to pathogens, two different experimental culture conditions were analysed. In the first, monocyte-depleted nylon wool non-adherent (NW) cells from healthy donors were stimulated with autologous MM preinfected with BCG (intracellular BCG). In the second, the NW cells were directly incubated with BCG, which was therefore extracellular. In the presence of MM, CD4 + T lymphocytes were the cell subset mainly expressing the activation marker, CD25, and proliferating with a peak after 7 days of culture. In contrast, in response to extracellular BCG, the peak of the proliferative response was observed after 6 days of stimulation, and CD56 + CD3 -cells (NK cells) were the cell subset preferentially involved. Such proliferation of NK cells did not require a prior sensitization to mycobacterial antigens, and appeared to be dependent upon contact between cell populations and bacteria. Following stimulation with extracellular BCG, the majority of interferon-c (IFN-c)-producing cells were NK cells, with a peak IFN-c production at 24-30 hr. Interleukin (IL)-2 and IL-4 were not detectable in NK cells or in CD3 + T lymphocytes at any time tested. IL-12 was not detectable in the culture supernatant of NW cells stimulated with extracellular BCG. Compared to the non-stimulated NW cells, the NW cells incubated for 16-20 hr with BCG induced the highest levels of expression of apoptotic/death marker on the NK-sensitive K562 cell line. BCG also induced expression of the activation marker, CD25, and proliferation, IFN-c production and cytotoxic activity, on negatively selected CD56 + CD3 -cells. Altogether, the results of this study demonstrate that extracellular mycobacteria activate several NK-cell functions and suggest a possible alternative mechanism of NK-cell activation as the first line of defence against mycobacterial infections.

Bovine NK Cells Can Produce Gamma Interferon in Response to the Secreted Mycobacterial Proteins ESAT-6 and MPP14 but Not in Response to MPB70

“…The findings of Vankayalapati et al supported a role for NK cells as a link between the innate and adapted immune response when they demonstrated that human NK cells regulated CD8 ϩ T-cell effector function in response to Mycobacterium tuberculosis (42). A direct effect of mycobacteria on NK cells was also recently described by Esin et al (14). They demonstrated that NK cells responded to extracellular BCG with proliferation, IFN-␥ production, and cytotoxicity.…”

Essential Roles of Monocytes in Stimulating Human Peripheral Blood Mononuclear Cells with Lactobacillus casei To Produce Cytokines and Augment Natural Killer Cell Activity

“…Moreover, it was previously reported that NK cells mainly secreted IFN-␥ when PBMNC were stimulated with Staphylococcus aureus (40). Esin et al (6) previously showed that NK cells could respond directly to Mycobacterium bovis bacillus CalmetteGuérin and produced IFN-␥ when monocytes were depleted from PBMNC. In the case of the response to nonpathogenic Lactobacillus johnsonii, NK cells secreted IFN-␥ effectively in the presence of monocytes (7).…”

Acute Immune Response toMycobacterium massiliensein C57BL/6 and BALB/c Mice

“…Whether this increase in NK cell frequency has a role in the immune response induced by M. massiliense infection requires further investigation (i.e., using IL-15 KO mice). Our previous studies on M. tuberculosis infection have shown that NK cells can produce IFN-␥ early in the response; however, NK cells are not crucial for the induction of Th1-mediated immune responses or the control of bacterial load (16,24).…”