Induction of Human T Cells That Coexpress CD4 and CD8 by an Immunomodulatory Protein Produced by Actinobacillus actinomycetemcomitans

Abstract

Actinobacillus actinomycetemcomitans, a gram-negative, capnophilic bacterium, is associated with several human diseases and is the suspected etiologic agent in certain forms of periodontal disease. We have previously shown that this organism produces an immunosuppressive factor (ISF) which is capable of inhibiting both T- and B-cell activation. Furthermore, these effects appear to be associated with the activation of a population of suppressor cells. We now report that the ISF induces a unique population of CD4+CD8+ dual-positive T-cells. By utilizing multiparameter flow cytometric analysis, we were able to detect the presence of dual-positive cells in cultures of human T-cells treated with PHA and ISF. The cells appeared within 48 hr and their induction was dependent upon the presence of both CD4 and CD8 cells in the culture. Dual expression of CD4 and CD8 was stable in that the cells continued to express both surface proteins after being sorted and cultured for an additional 24 hr. Phenotypic analysis indicates that these cells are also CD3+, CD2+, CD5+, TCRαβ+, CD45RA+ (and RO+), and CD29+. The dual-positive cells express surface markers associated with Tcell activation: CD25+, CD69+, CD71+, and HLA-DR+. In contrast, the cells were negative for CD34, CD57, CD56, and CD16. Cell cycle analysis indicates that >80% of the dual-positive cells were in the S phase. Finally, functional analyais of these cells indicates that they are capable of suppressing the proliferative response of autologous T-cells to PHA.