Induction of human TCRγδ+ and TCRγδ− CD2 + CD3 − double negative lymphocytes by bacterial stimulation

Abstract

When human blood mononuclear cells (MNC) were incubated with heat-killed bacteria, proliferation of MNC was observed 5 days after stimulation, showing a peak on day 7. interestingly, the bioassay of the culture supernatant and Northern blot analysis of mRNA demonstrated that no IL-2 production was associated with these proliferative responses. The induced lymphoblasts consisted predominantly of TCRγδ⁺ (22.4 ± 9.3%) and TCRγδ⁻ CD2⁺CD3⁻ (33.2 ± 11.8%) double negative lymphocytes (n = 10), which were initially minor populations (< 10%) in freshly isolated MNC. The prominent induction of TCRγδ⁺ cells was confirmed by Northern blot analysis. TCRγδ⁺ cells induced by bacterial stimulation seemed to generate from lymphocytes lacking the apparent expression of γδ TCR. The inducing capability for double negative cells is present in a large number of species of bacteria, especially Gram-positive bacteria. Gel filtration analysis of ultrasonicated filtrates of Staphylococcus aureus and Streptococcus pyogenes revealed that a substance with an M, of 25–26 kd could be substituted for whole bacterial particles in the cell proliferative responses. In contrast to the purified protein derivative (PPD)-induced response, the response described here was inducible in the cord blood of neonates who had not yet been exposed to the corresponding bacterial infection. The physicochemical properties of the sonicated filtrates were different from those of PPD. These results suggested that the present phenomenon may be nonspecific, polyclonal (or oligoclonal) activation of TCRγδ⁺ and TCRγδ⁻ CD2⁺CD3⁻ cells by bacterial stimulation.