Endogenous heat shock protein GroEL of A. actinomycetemcomitans preferentially targets primary human CD8+ T cells

Abstract

Apoptosis can be used to manipulate host cells by bacterial products such as bacterial heat shock proteins (Hsp). One of the virulence factors of periodontal pathogen Aggregatibacter actinomycetemcomitans is heat shock protein GroEL (AaGroEL), which has been shown to interact with host cells. AaGroEL (Hsp64) also has the potential to modulate immune system cells. In this study we used endogenous AaGroEL protein as an antigen to study bacterial Hsp-induced apoptosis in different immune system cells. Human peripheral blood mononuclear cells and cell lines were cultured with different doses (50-1000 ng/mL) of endogenous AaGroEL at various time points. Apoptosis of the cells was measured by Annexin V and 7AAD labeling. Apoptotic cells were analyzed by flow cytometry. Our data suggested that AaGroEL-responding primary CD8+ T cells were more susceptible to apoptosis than CD4+ T cells. Furthermore, the magnitude of apoptosis in the Jurkat T cell line was higher than that in primary CD8+ T cells. There was no statistically significant level of apoptosis in the chronic myeloid leukemia (K562) cell line, which belongs to myeloid lineages. Thus, A. actinomycetemcomitans GroEL protein has more potent apoptotic effect on cells that are derived from a lymphoid progenitor.