Role of Ia Antigen Expression and Secretory Function of Accessory Cells in the Induction of Cytotoxic T Lymphocyte Responses Against Herpes Simplex Virus

ABSTRACT

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 P388D₁ 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⁺ P388D₁ 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⁺ P388D₁ 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⁻ P388D₁ 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.