The lymphoreticular system in triggering virus plus self-specific cytotoxic T cells: evidence for T help.

Abstract

The thymus determines the spectrum of the receptor specificities of differentiating T cells for self-H-2; however, the phenotypic expression of T cell's specificity for self plus virus is determined predominantly by the H-2 type of the antigen presenting cells of the peripheral lymphoreticular system. Furthermore, virus specific helper T cells are essential for the generation of virus-specific cytotoxic T cells. For cooperation between mature T cells and other lymphocytes to be functional in chimeras, thymic epithelial cells and lymphohemopoietic stem cells must share the I region; killer T-cell generation also requires in addition compatibility for at least one K or D region. These conclusions derive from the following experiments: A leads to (A X B)F1 chimeric lymphocytes do produce virus-specific cytotoxic T-cell activity for infected A but not for infected B cells; when sensitized in an acutely irradiated and infected recipient (A X B)F1 these chimeric lymphocytes respond to both infected A and B. Therefore the predominantly immunogenically infected cells of chimeras the radiosensitive and by donor stem cells replaced lymphoreticular cells. In this adoptive priming model (KAIA/DB leads to KAIA/DC) chimeric lymphocytes could be sensitized in irradiated and infected F1 against KA and DC but not against infected DB targets. In contrast KBIB/DA leads to KCIC/DA chimeras' lymphocytes could not be sensitized at all in appropriately irradiated and infected F1 recipients. Thus these latter chimeras probably lack functional I-specific T helper cells that are essential for the generation of T killer cells against infected D compatible targets. If T cells learn in the thymus to recognize H-21 or K, D markers that are not at least partially carried themselves in other cells of the lymphoreticular system immunological interactions will be impossible and this paradox situation results in phenotypic immune incompetence in vivo.

Distinct Ir genes for helper and killer cells in the cytotoxic response to H-Y antigen.

“…This does not mean that help would be required in CTL responses to all other antigens as well. We found that in completely allogeneic chimeras excellent CTL responses to H-2 antigens were obtained which, according to the suggestion of Zinkernagel et al (8), would be independent of T-cell help. …”

Helper T cells for cytotoxic T lymphocytes need not be I region restricted

“…Nonetheless, on the basis of mostly indirect results from a variety of experimental approaches, the most prevalent model of CTL activation is one that closely parallels models of B cell activation, i.e., that I regionrestricted helper T cells activated by interaction with antigen in the context of I region determinants deliver inducing signals to antigen-activated precursor CTL (1)(2)(3)(4)(5). In some models, the helper T cell interacts with CTL precursors via the restricted recognition of I region determinants expressed by the CTL precursor (1,2).…”

“…Nonetheless, on the basis of mostly indirect results from a variety of experimental approaches, the most prevalent model of CTL activation is one that closely parallels models of B cell activation, i.e., that I regionrestricted helper T cells activated by interaction with antigen in the context of I region determinants deliver inducing signals to antigen-activated precursor CTL (1)(2)(3)(4)(5). In some models, the helper T cell interacts with CTL precursors via the restricted recognition of I region determinants expressed by the CTL precursor (1,2). Experiments interpreted as supporting the role of I region-recognition events during the process of CTL induction include (a) studies demonstrating the augmentation of CTL responses to foreign H-2K and D antigens by I region-reactive T cells (5,6), (b) studies of CTL responses to viral (2) or non-H-2 cell surface antigens (7) or hapten (8), demonstrating an influence of I region genes expressed by cells of the thymus on the response phenotype of T cells that mature therein, (c) a study demonstrating the apparent depletion, by in vivo negative selection procedures, of I region-restricted helper cells required for an in vitro secondary CTL response specific for minor histocompatibility antigens (9), and (d) the finding that Ia + non-T accessory cells are required for in vitro CTL responses (4, 10, 1 1).…”

“…In some models, the helper T cell interacts with CTL precursors via the restricted recognition of I region determinants expressed by the CTL precursor (1,2). Experiments interpreted as supporting the role of I region-recognition events during the process of CTL induction include (a) studies demonstrating the augmentation of CTL responses to foreign H-2K and D antigens by I region-reactive T cells (5,6), (b) studies of CTL responses to viral (2) or non-H-2 cell surface antigens (7) or hapten (8), demonstrating an influence of I region genes expressed by cells of the thymus on the response phenotype of T cells that mature therein, (c) a study demonstrating the apparent depletion, by in vivo negative selection procedures, of I region-restricted helper cells required for an in vitro secondary CTL response specific for minor histocompatibility antigens (9), and (d) the finding that Ia + non-T accessory cells are required for in vitro CTL responses (4, 10, 1 1). In addition, studies of the Ir gene defect ofnonresponder strains in the CTL response of female mice to the male antigen, H-Y, have been interpreted in terms of I region-restricted helper T cells (1,7,(12)(13)(14)(15).…”

Effect of Age on Immune Function in Terms of Chemically Induced Cancers

“…A gene regulating testosterone metabolism is linked to the major histocompatibility complex (H-2) of the mouse (72). Finally, during differentiation of T cells, the ability to recognize "self" versus "'nonself" with respect to the ability to respond normally to virus infections is determined by the thymic epithelial cells and not other cells of the body (73). These epithelial cells are the source of the thymic hormones.…”