Generation of cytolytic T lymphocytes in vitro. XI. Accessory cell requirement in secondary responses to particulate alloantigen

Suppression of cytolytic T-lymphocyte responses through inactivation of non-T accessory cells

The suppressive properties of nonspecific cytotoxic T lymphocyte (CTL) populations, derived from murine fetal calf serum (FCS)-precultured cells expanded in interleukin 2 (operationally defined as FCS-CM-expanded cells), were investigated on CTL responses generated by syngeneic alloreactive lymphoid cells. Our results suggest that the addition of FCS-CM-expanded cell populations can inhibit the CTL response by elimination of the bone marrow-derived macrophage (BM M phi) population used as non-T accessory cells. Indeed, in the culture conditions used, removal of IL-2 by the FCS-CM-expanded cells as well as a direct inactivating effect on the CTL precursors (CTL-P) could be excluded as a reason for inhibition. On the other hand, we were able to show that the BM M phi population was very sensitive to the cytolytic activity exhibited by the inhibiting cells in a 3 h 51Cr-release assay and that the suppressor effect observed could be partially circumvented by a second addition of BM M phi on the second day after the initiation of the culture.

Role of Ia antigen expression and secretory function of accessory cells in the induction of cytotoxic T lymphocyte responses against herpes simplex virus

Splenocytes from mice which have been primed in vivo with herpes simplex virus type 1 (HSV-1) can be restimulated in vitro with infectious or UV-inactivated HSV-1 to generate HSV-specific, H-2-restricted cytotoxic T lymphocytes (CTL). HSV-primed splenocytes which have been depleted of adherent cells by sequential incubation on plastic, nylon wool, and Sephadex G-10 are not able to respond with a CTL response when restimulated in vitro. A variety of Ia-positive and Ia-negative (Ia(+) and Ia(-)) cell populations were assessed for their ability to supply accessory cell functions to spleen cells which had been exhaustively depleted of adherent cells, as measured by the restoration of a CTL response to HSV-1. Of these, only those populations which included Ia(+) cells were capable of providing accessory cell function. The ineffective populations were devoid of Ia antigens, except for B lymphocytes, which are Ia(+) and still incapable of serving as accessory cells. Splenic adherent cells and resident peritoneal cells were both proficient at restoring anti-HSV CTL responses, although splenic adherent cells were clearly superior at limiting cell numbers. Neither population was capable of accessory cell activity, however, if it was pretreated with anti-Ia antiserum plus complement or if anti-Ia serum was present during induction. Peritoneal cells lose virtually all of their membrane-associated Ia antigen after a brief period of in vitro culture (24 to 48 h). Cultured peritoneal cells, as well as P388D(1) cells (normally Ia(-)), can be induced to express Ia antigens within 48 h if they are cultured with concanavalin A-stimulated spleen cell supernatants. Ia(+) P388D(1) cells without the extraneous macrophage factor are not able to restore CTL responsiveness to HSV-1 in vitro, whereas Ia(+) cultured macrophages are fully competent accessory cells. When Ia(+) P388D(1) cells were supplemented with the macrophage-derived soluble factor interleukin 1, they displayed a modest, but significant, capacity to restore secondary anti-HSV CTL responses. In addition, glutaraldehyde-fixed, HSV-1-infected Ia(+) peritoneal cells, which could not restore the CTL response alone, were capable of providing accessory cell function if extraneous interleukin 1 was provided. In contrast, Ia(-) cultured peritoneal cells, Ia(-) P388D(1) cells, and various other Ia(-) cell lines were unable to participate in the generation of CTL even in the presence of interleukin 1. The adherent cell population would therefore appear to be making at least two essential contributions to the process of CTL development, namely, the secretion of interleukin 1 and the presentation of antigen in the context of membrane-associated Ia antigen.

Suppressive effect by cooperation of splenic and peritoneal adherent cells on generation of cytotoxic T lymphocytes

When spleen cells primed in vivo against allogeneic lymphoid cells were used as responder cells in secondary mixed lymphocyte cultures, a high degree of cytotoxicity was generated even in the absence of splenic adherent cells. However, removal of adherent cells from such primed responder spleen cells reduced the cytotoxicity to some extent. On the other hand, when these responder cells were transferred into the peritoneal cavity of irradiated syngeneic mice together with antigenic cells, unseparated responder cells generated a lower degree of cytotoxicity than did adherent cell-depleted responder cells. In an in vitro system, peritoneal adherent cells also suppressed the generation of cytotoxic T lymphocytes by unseparated responders; however they augmented the cytotoxic T lymphocyte generation by adherent cell-depleted responders. These adherent cell populations with augmenting activity became inhibitory when they coexisted. The mechanism of this inhibitory action remains unclear.