Antigen-presenting cells for CD8+ T cells

Evidence is presented that a wide variety of cell types are capable of presenting class I alloantigens to purified unprimed CD8+ cells in the absence of added help. These cells include dendritic cells, a population of Ia- Thy 1- cells in spleen, peritoneal exudate cells and one of three T-tumor lines. Some cell types, e.g. T-blast cells and overnight-adherent peritoneal exudate cells (OA-PEC) only expressed antigen-presenting cell (APC) function in the presence of added lymphokines. Stimulation of OA-PEC with small concentrations of lipopolysaccharide or treatment of T-blast cells with neuraminidase (N'dase) strongly enhanced the APC function of these cells and led to helper-independent responses. N'dase treatment of small resting T stimulators caused partial restoration of APC function: strong responses were observed but only in the presence of exogenous lymphokines. Studies with T-tumor lines preincubated with IFN-gamma suggested that APC function correlates closely with antigen (class I) expression. Collectively, the data support the view that APC function depends upon a multiplicity of factors including antigen density, the level of accessory (adhesion) molecules and net surface charge. It is suggested that the potency of APC function is largely a reflection of the overall avidity of T-APC interaction: high-avidity binding leads to helper-independent responses whereas weaker binding results in helper-dependent responses.