RESUMEN
Experiments were conducted in an effort to determine the ability of B and T lymphocytes to serve as APC for the activation of HSV-primed splenic T cells to become class I-restricted, HSV-specific CTL. The results showed that both freshly isolated splenic B cells as well as LPS and dextran sulfate (L/D)-activated B cells were effective at stimulating the generation of CTL during a 5-day in vitro culture. There was no requirement for the addition of exogenous IL-2 to the culture and, since murine B cells do not appear to express either membrane or secreted IL-1, this lymphokine appears to either not be required for the activation of virus-specific CTL or to be provided by the T cells themselves. When normal B cells were separated into fractions enriched for resting vs activated cells and then tested for their ability to stimulate the generation of HSV-specific CTL, it was found that while the activated B cells were quite effective at stimulating the generation of CTL, resting B cells were ineffective at carrying out this function. In contrast to normal B cells, normal T cells were unable to act as APC. However, Con A-activated T lymphoblasts were equivalent to L/D B cells in their ability to mediate the generation of CTL activity. L/D B cells that had been pulsed with HSV and then incubated at 37 degrees C for greater than 1 h could be fixed with paraformaldehyde and were still able to function as APC. The finding that L/D B cells, that had been fixed at 1 h or less after exposure to HSV, were unable to function as APC suggested that either active Ag "processing" steps may be required for the presentation of Ag in the context of class I molecules or that there is a requirement for the synthesis of viral protein Ag before presentation.
Asunto(s)
Células Presentadoras de Antígenos/inmunología , Linfocitos B/inmunología , Simplexvirus/inmunología , Linfocitos T Citotóxicos/inmunología , Linfocitos T/inmunología , Animales , Linfocitos B/clasificación , Activación de Linfocitos/efectos de los fármacos , Ratones , Ratones Endogámicos CBA , Mitógenos/farmacología , Cavidad Peritoneal/citologíaRESUMEN
In this study we have evaluated some of the potential mechanisms that may be responsible for the inefficiency with which resting B cells function as antigen-presenting cells (APC) and the mechanism by which that function is enhanced following treatment of B cells with neuraminidase. One mechanism that has been previously suggested is that glycosylation differences in Ia associated with different APC accounts for the different functional capacities of resting and activated B cells. It has been postulated that removal of sialic acid from resting B cell Ia results in a correction of its antigen-presenting defect. To study this possibility, we have used purified I-Ad from different B cell sources in a planar membrane system to present an immunogenic peptide of chicken ovalbumin (Ova) to an I-Ad-restricted Ova-specific T cell hybridoma. It was found that I-Ad isolated from resting B cells, B cell stimulatory factor 1 (BSF-1) or lipopolysaccharide and dextran sulfate-stimulated B cells, or A20 B lymphoma cells were all equivalent in their antigen-presenting capacity. Furthermore, removal of sialic acid from Ia did not enhance its capacity to serve as a restriction element. The mechanism by which neuraminidase treatment enhances B cell APC function was further investigated by studying the effect of sialic acid removal on a primary mixed leukocyte reaction (MLR). When allogeneic fixed B cells were used as stimulator cells it was found that neither resting nor BSF-1-stimulated B cells could induce a MLR. Following neuraminidase treatment, BSF-1-treated B cells, but not resting B cells, were capable of stimulating a MLR. However, a MLR was also stimulated by allogeneic BSF-1-treated B cells when the responder T cells, rather than the stimulator cells, were treated with neuraminidase. An enhancing effect similar to that obtained by neuraminidase treatment could be obtained by the addition of 2% polyethylene glycol to the MLR culture. These data suggest that the inability of BSF-1-stimulated cells to function efficiently as accessory cells in stimulating a primary MLR is due to their relative inability to interact physically with T cells, a deficiency that is overcome by neuraminidase treatment of either T or B cell populations or by the addition of polyethylene glycol to the culture. Although the reason for the failure of these same treatments to restore the accessory cell function of resting B cells is not known, some possible mechanisms are discussed.