Cell-mediated immunity to vesicular stomatitis virus infections in mice.

The T cell-mediated immune responses of mice against vesicular stomatitis virus (VSV) were assessed by measuring direct primary foot pad swelling after local VSV infection and cytotoxic activity in spleens. The cytolytic activity was mediated by T cells since it was anti-theta + complement sensitive, was restricted by the K and D region but not the I region of H-2 and rapidly increased after 4 days but decreased 8 days after systemic or local infection. Cytolytic activity was virus-specific as reciprocally tested with VSV and vaccina virus immune T cells. Measurable activity on day 7 depended on infectious virus dose, virus virulence, and non-H-2 genetic background of the host. More than half of the cytolytic activity wasblocked specifically by either immune anti-H2 or rabbit anti-VSV antisera. Analysis of the kinetics of appearance of antigenic changes using metabolic inhibitors, revealed that the changes that rendered target cells susceptible to lysis after infection, occurred within the first hour after infection.     

Chemical biology: Paper alert

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in chemical biology.     

Cell-mediated immune response to lymphocytic choriomeningitis and vaccinia virus in rats.

The parameters of cell-mediated immune responses of rats to infection with lymphocytic choriomeningitis virus or vaccinia virus were assessed by measuring primary footpad swelling, increased weights of the local lymph nodes, increased numbers of lymphocytes per lymph node, and the course of virus-specific cytolytic activity by these lymphocytes. Except for lack of a defined swelling caused by vaccinia virus injected into the hind footpads of rats, the kinetics of all these responses correlated and were in accord with the usual time course of cellular immune responses. Starting 3 days after infection, peaking at 5 to 7 days, and disappearing after 10 to 12 days, the responses by rats to both viruses were comparable to those found in mice. The phagocytes of these infected rats inhibited the growth of Listeria monocytogenes in vivo, indicating activation of the macrophages by virus-specific cellular immunity. The rat cytotoxic lymphocytes were thymus derived as judged by various criteria: inactivation by an absorbed rabbit anti-rat brain antiserum plus C, susceptibility to anti Thy 1.1 plus C, restriction of the lytic activity within inbred strains and probably by the Ag-B locus, and the kinetics of the response. The cytotoxic T lymphocytes were virus specific since they killed only target cells infected with the same virus but not uninfected cells, or targets that were infected with an unrelated virus.     

Discrepancy between in vitro measurable and in vivo virus neutralizing cytotoxic T cell reactivities. Low T cell receptor specificity and avidity sufficient for in vitro proliferation or cytotoxicity to peptide-coated target cells but not for in vivo protection.

The TCR-alpha beta of CTL recognize peptide Ag in association with MHC class I molecules. TCR binding should be highly specific to guarantee pathogen specificity and to avoid self-reactivity. Therefore, the in vivo relevance of T cells exhibiting cross-reactivities in vitro and the respective role of the TCR affinities involved are not clear. To analyze high and low avidity T cell activities both in vitro and in vivo, we investigated primary and clonal CTL responses specific for the lymphocytic choriomeningitis virus nucleoprotein 118-126 epitope in association with the two closely related H-2Ld or H-2Lq molecules. As expected, we found highly specific class I-allele-restricted CTL responses when antiviral protection or immunopathology in vivo and lysis of virus infected target cells in vitro were analyzed. In contrast, the CTL were MHC crossreactive and thus considerably less discriminatory against targets expressing high MHC-peptide densities and in proliferation assays. The data show that relatively high TCR avidities are required for virus neutralization in vivo, in contrast to in vitro analyses of peptide-coated target cells or proliferative T cell responses that may engage TCR of low avidity and broad specificity and therefore may not reflect biologically relevant TCR avidities.     

Role of the H-2I region in the generation of an antiviral cytotoxic T-cell response in vitro

The participation of H-2I gene products in generating virus-specific proliferative and/or cytotoxic T-lymphocyte (CTL) responses was investigated. Spleen cells from mice infected with vaccinia virus were restimulated secondarily in vitro with syngeneic virus-infected peritoneal exudate cells (PEC) and then restimulated in tertiary cultures with virus-infected PEC from syngeneic and partially histoincompatible strains of mice. Based on the finding that comparable proliferative responses resulted when stimulating the responding cells were histocompatible at the H-2K, I, or D region of the major histocompatibility complex (MHC), the additively enhanced, but not potentiated, proliferation caused by identity at two or three H-2 regions was analyzed. Enhancement of proliferation followed when the H-2K/D components plus virus and the H-2I components plus virus were either on the same, or alternatively on two, stimulating cells. This suggests that H-2K, D, and I plus virus trigger distinct T-cell subsets. A virus-specific CTL response was generated in vitro when spleen cells from virus-primed mice and even unprimed mice were stimulated with cells sharing only H-2K and/or H-2D of the MHC. Identity at the H-2I region did not stimulate a CTL response, nor did it influence the magnitude of the $\text{K}\text{D}$ restricted response. Nevertheless, the presence of anti-Ia antiserum in cultures of syngeneic stimulators and responders inhibited the cytotoxic response to a great extent. Therefore, H-2I region products seem to participate in the generation of virus-specific CTL in vitro.