T J Braciale

Antigen Presentation Pathways to Class I and Class II MHC‐Restricted T Lymphocytes

Our observations on the cellular immune response to type-A influenza suggest the existence of two distinct pathways of protein antigen presentation to T lymphocytes. One of these pathways is involved with presentation of antigens introduced into the presenting cell from without. This exogenous presentation pathway is the well-recognized route of presentation of soluble and particulate antigens to T lymphocytes. This pathway probably involves uptake of antigen into endocytic vesicles, alteration of antigen within an intracellular compartment, and subsequent display of antigen on the presenting cell surface (Unanue 1984). The second pathway is one which we have tentatively designated as an endogenous presentation pathway. The constraints on this pathway have yet to be fully defined. At a minimum, this pathway appears to involve the presentation of antigens which are synthesized de novo in the presenting cell utilizing the cells biosynthetic machinery. This pathway may also handle preformed antigens located within the cytosolic compartment of the presenting cell. Perhaps the most striking feature of these two antigen presentation pathways is the close association between the MHC restriction of an antigen-specific T lymphocyte and the pathway of antigen presentation to that T lymphocyte. Our data suggest that this association holds both at the effector level and at the level of induction of T lymphocytes. Thus, presentation of a given antigen by the endogenous pathway preferentially triggers a response from class I MHC-restricted T lymphocytes directed to that antigen. The molecular basis for this link of class I MHC-restriction to the endogenous pathway and MHC class II restriction to the exogenous pathway is unknown. It seems likely that interactions between MHC molecules and antigen within the presenting cell may be critical for the demarcation of these pathways. Thus, for example, antigen presented by the endogenous route may only be able to associate intracellularly with newly synthesized or recycling class I MHC molecules. An understanding of the molecular basis of this phenomenon will require detailed information on the expression, intracellular trafficking, and transport of class I and class II MHC molecules in the antigen-presenting cell. An unresolved issue, at least in the case of viral antigens, is the nature and form of the antigenic moieties presented by the exogenous and endogenous pathways. In the case of viral antigen presentation to class II MHC-restricted T lymphocytes, there is strong, albeit indirect, evidence for processing of antigen and recognition of fragments of viral polypeptides (Lamb et al. 1982, Hackett et al. 1983).(ABSTRACT TRUNCATED AT 400 WORDS)

Influenza virus-specific human cytotoxic T cell clones: Heterogeneity in antigenic specificity and restriction by class II MHC products

Human cytotoxic T lymphocytes specific for A/JAP/57 (H2N2) influenza virus were cloned from in vitro stimulations of peripheral blood lymphocytes. Analysis of the viral specificity in cytotoxic function revealed one clone that killed all type A influenza-infected targets, another clone that was specific for the hemagglutinin subtype of the immunizing influenza virus, and the third clone that demonstrated cytotoxicity restricted to the hemagglutinin of A/JAP/57 and A/JAP/62 (H2N2) and not other type A influenza strains with the H2N2 subtypes. The phenotype of these three clones was Leu 2-, Leu 3+, Leu 4+; MHC restriction of their cytotoxic function was mapped to HLA-DR by a panel of target cells as well as by inhibition of cytotoxicity with monoclonal antibodies. Proliferation of these clones, examined in a tritiated thymidine incorporation assay, was found to be driven by antigen in the absence of exogenous lymphokines. For all three clones antigen-dependent production and secretion of lymphokines with IL-2 activity was demonstrated. The antigen specificity of proliferation and factor production was shown to be identical to the pattern that each clone revealed in its cytotoxic function.

Macrophage procoagulant-inducing activity of influenza-specific effector T cells

Three different types of immune mouse T cells raised against influenza virus were tested for their ability to induce the formation of macrophage procoagulant activity (MPCA) by a macrophage cell line PU5-1.8. They were primary spleen cells, taken 6 days after iv injection of virus, spleen cells from sensitized mice challenged with virus and cultured in vitro for 5 days (secondary cultured cells), and cloned T cells. With the last two preparations, some samples were K,D region restricted, Lyt 2+, and had cytotoxic activity; other samples were I region restricted, Lyt 2-, and were not cytotoxic. Samples of a concanavalin A-activated T-cell supernatant which regularly induced MPCA with PU5-1.8 cells were included as controls in all assays. A few batches of T-cell preparations failed to induce MPCA production, however, most batches were active. Two sources of variation were detected: first, the number of cells (5- to 150-fold) needed to induce a certain level of MPCA, as measured by the decrease in clotting time; and second, the value of the gradient of the cell dose response. Both K,D- and I-region-restricted cells, either as cloned or secondary cultured cells, could induce MPCA but with the latter preparation, I-region-restricted cells were the better inducers by about eightfold. T cells tested in this way were also injected into mouse hind footpads and their ability to mediate delayed-type hypersensitivity (DTH) reactions was measured. A positive but not proportional correlation between the abilities to induce MPCA and mediate DTH activity for primary spleen cells was found, but this was not generally observed with cultured or cloned T cells.

Pretreatment of Stimulator/Target Cells with Xyloside Inhibits Synthesis of the Class II Associated Proteoglycan, but Potentiates an MLR and Antigen Presentation

HLA class II molecules are associated with a number of invariant chain glycoproteins including γl or Ii, the ~ 31 Kd predominant form of invariant chain; the ~ 33 Kd species γ2 and γ3; the 41 Kd species p41, the 25 Kd species, p25; and a number of acidic forms. In addition, we demonstrated that the class II molecules are also associated with a 40–70 Kd chondroitin sulfate proteoglycan molecule (CSPG) (1), and further demonstrated that the core protein of the CSPG is Ii (2).

CTL Recognition of Transfected H-2 Gene and Viral Gene Products

The host response to viral infection consists of both virus-specific and nonspecific elements. Among the specific (immune mediated) responses to viral infection, several lines of evidence point toward the cytolytic T lymphocyte (CTL) as an important effector in antiviral immunity [1]. Notably, specific antiviral cell-mediated cytolytic activity is readily demonstrable during the course of many experimental viral infections [2]. More importantly, both heterogeneous and cloned populations of antiviral CTL have been shown, upon adoptive in vivo transfer into infected recipients, to specifically inhibit virus replication and to alter the outcome of lethal infection [2–5]. Because the antiviral activity of this T lymphocyte subset is monitored in vitro by the capacity of sensitized CTL to directly destroy virally infected target cells by cell-to-cell contact [1], it is reasonable to assume that CTL would function in a similar manner in vivo to eliminate virus, i.e., by direct destruction of infected cells. However, antiviral CTL have also been shown to release lymphokines, including interferon-γ (IFNγ), after contact with antigen [6]. Thus, CTL may inhibit, through a variety of mechanisms (both antigen-specific and nonspecific), virus replication and spread in the body [7].