Human T cells express CD86 and acquire APC function after stimulation with human or porcine APC

Abstract

The interaction between CD86, expressed on antigen presenting cells (APCs), and CD28 on T cells is critical for T cell activation. It has been shown that stimulation of peripheral blood lymphocytes with anti-CD3 and IL-2 induces CD86 expression on T cells, which are capable of providing costimulation to naı̈ve T cells in a human allogeneic system. The goal of our experiments was to determine whether human or porcine APCs can induce CD86 expression on human T cells and whether these T cells can function as APCs. Method: CFSE-labeled human T cells were co-cultured with human or porcine APCs. At day 5, the cultures were harvested and stained with labeled CD86, CD80, CD25 and anti-HLA-DR, CD4, CD8 and TOPRO-3 (viability probe). The samples were analyzed by four-color flow cytometry. Furthermore, T cells were isolated from cultures stimulated with anti-CD3 and Il-2, human APC or Pig APC and these cells were fixed with 1% paraformaldehyde. These cells were used to stimulate fresh syngeneic or allogeneic CFSE-labeled human T cells and these cultures were analyzed at day 7 by flow cytometry. Results: At day 5, cultures stimulated with anti-CD3 and IL-2, allogeneic APCs or porcine APCs show a high percentage (>50%) of proliferating cells expressing CD86 whereas few (2%) non-proliferating cells express CD86. The proliferating cells also expressed CD80, CD25, CD54, Class II and CD45RO. CFSE profiles indicated that fixed T cells expressing CD86 induced by these routes trigger the proliferation of both allogeneic and syngeneic T cells. However, 3H-Thymidine incorporation at day 7 was negative. Conclusion: Human T cells, in response to human or porcine APC stimulation, express CD86 and Class II molecules and function as APCs as assessed by CFSE proliferation assays. Thymidine incorporation data indicates that proliferation had ceased by day 7. This is most likely explained by activation-induced cell death at this time point, since, the proliferating T cells show high levels activation markers CD25 (IL-2R) and CD54 (ICAM-1) and are of memory phenotype (CD45RO positive).