The cellular compartmentalization of macrophage-associated nominal antigen: immunologically relevant macrophage-associated antigen may not require an intracellular phase of macrophage handling

Processing of viral antigens and presentation to class II-restricted T cells

Some antigens require intracellular processing by antigen presenting cells before being presented to T cells in conjunction with surface major histocompatibility complex antigens. The whole mechanism of these processing events is not known and in this article, Kingston Mills puts forward arguments for alternative routes of antigen processing, with particular reference to recognition of viral proteins by class II-restricted T-cell clones.

Binding of antigen to Ia molecules on intact antigen presenting cells demonstrated by photoaffinity labeling

We used a photoaffinity labeling technique to investigate whether a molecular interaction occurs between antigen and Ia molecules on antigen presenting cells (APC) in the absence of T lymphocytes. M.12.4.1 B lymphoma cells (Iad), which are able to present bovine insulin to Iad lymph node primed T cells, were given radioiodinated bovine insulin derivatized with the photoreactive group (2-nitro-4-azidophenylacetyl) at Lys 29 of the B chain of the insulin molecule. Processing of insulin was allowed by incubating the APC with antigen for increasing periods of time at 37 degrees C or 4 degrees C. The covalent coupling of the processed photoreactive antigen to any neighboring cellular protein was thereafter induced by u.v. irradiation. Immunoprecipitation of membrane proteins by monoclonal antibodies showed that under these conditions, the alpha and beta subunits of the Ia molecules were selectively photolabeled. Labeling was time- and temp-dependent as was the internalization of insulin. The apparent mol. wts of the antigen-Ia molecule complexes were not significantly different from that of native Ia molecules radioiodinated by surface labeling, indicating that only a small fragment of the antigen was covalently coupled to Ia molecules. Similar experiments performed with human B lymphoma cells (526 cells) gave similar results. These observations therefore indicate: (1) that Ia molecules expressed by intact APC are able to bind antigens in the absence of T lymphocyte antigen receptor; and (2) that this association, at least for insulin, requires uptake and a proteolytic fragmentation of the antigen by the APC.

Expression of herpes simplex virus glycoprotein D on antigen presenting cells infected with vaccinia recombinants and protective immunity

We studied the effect of the temporal regulation of herpes simplex virus (HSV) type 1 glycoprotein D (gD-1) expression in Ia+ epidermal cells (EC) and macrophages on virus specific immunity and protection from HSV-2 challenge. gD-1 was expressed on the surface of cells infected with a vaccinia recombinant containing gD-1 under the control of an early vaccinia virus promoter (VP176). It was not expressed in cells infected with a recombinant (VP254) in which gD-1 is controlled by a late vaccinia virus promoter. BALB/c mice immunized with both recombinants seroconverted to HSV-2 as determined by neutralization. However, HSV specific delayed type hypersensitivity (DTH) responses were significantly (p less than 0.025) higher in VP176 than VP254 immunized animals. Both VP176 and VP254 immunized mice were protected from severe neurological disease due to HSV-2 challenge at 14 days post immunization, but long term protection was observed only in VP176 immunized mice.

Differential requirements for the processing and presentation of soluble and particulate bacterial antigens by macrophages

The requirements for antigen processing and presentation by macrophages using various forms of antigens derived from Listeria monocytogenes have been studied. Antigen presentation was monitored by T cell-macrophage binding and interleukin production using T cells from Listeria monocytogenes-infected mice and specific T cell hybridomas. Antigen processing requirements were defined by three criteria: (a) inhibition by lysosomotropic agents, NH4Cl and chloroquine; (b) kinetic relationships between antigen uptake and antigen presentation; and (c) antigen presentation by macrophages pre-fixed with glutaraldehyde. In comparing heat-killed Listeria monocytogenes (HKLM) with soluble listerial proteins (SLP), the presentation of SLP was less sensitive to lysosomotropic agents, showed faster antigen processing kinetics than with HKLM and could occur using pre-fixed macrophages. Transitions between particulate and soluble forms had dramatic influences on processing requirements. Antigens associated with HKLM could be converted to soluble forms which did not require processing by preculture with macrophages and also by physical (e.g. sonication) and chemical (sodium dodecyl sulfate) treatments in the presence of protease inhibitors. Conversely, antigen processing was required when SLP were converted to a particulate form by covalent binding to latex beads. Analysis of SLP by molecular sieve chromatography and preparative SDS-polyacrylamide gel electrophoresis revealed that high molecular weight proteins (greater than 60 kDa) could be presented by prefixed macrophages without prior processing. We conclude that the transition from a particulate to soluble antigenic form can be a significant antigen processing event.

Activated human T cells can present denatured antigen

The requirements for activated, Ia-positive human T cells to present antigen were examined. Although activated T cells could present allo-Ia antigens, activated T cells could not present native, soluble protein antigens. We have now shown that activated T cells can present denatured protein antigens to stimulate proliferation of antigen-specific T-cell lines. Since denatured antigen may represent a processed form of antigen, the data suggest that activated T cells can present antigen but may not be able to process antigen as efficiently as other presenting cells. We have also shown that antigen-specific T-cell lines, which are also Ia positive, are able to present antigen to themselves, if the antigen is in a denatured form. Autopresentation requires a critical minimal cell number to stimulate proliferation, even with denatured antigen. The ability of activated T cells to present antigen may reflect an important amplification or feedback mechanism of immune regulation.

Antigen presentation by spleen dendritic cells

It is now recognized that dendritic cells (DC) isolated from mouse spleen play an important role in activating T lymphocytes. These DC, which show many similarities to veiled cells found in the paracortical regions of spleen and lymph node, may be closely related to the epidermal Langerhans cells. It is known that DC are extremely effective allostimulators. We have also found that although DC lack demonstrable phagocytic ability, they are extremely potent at presenting soluble polypeptide antigens to primed T cells. Since T lymphocytes comprise several distinct subsets (particularly cytotoxic, helper, and suppressor) in our most recent studies we have asked whether DC are able to trigger all these different subsets of T cells. We examined the ability of different spleen cell types coupled with the hapten NP to induce antigen-specific T suppressors for a delayed type hypersensitivity (DTH) response. It was found that T suppressors were generated only when hapten was conjugated to a spleen-derived antigen-presenting cell. Further analysis revealed that macrophages but not DC were able to induce defined sets of suppressor cells in vivo (although DC were able to trigger a very powerful DTH response). We also examined the ability of DC to activate T cells which are required to cooperate with B cells in the production of antibody. Even though DC were able to trigger T lymphocytes to produce lymphokines, these activated T cells did not act as helper cells in a standard hapten-carrier system. Possible mechanisms for this dichotomy of DC function are discussed.

Hapten-specific T-cell response to azobenzenearsonate-N-acetyl-L-tyrosine in the Lewis rat. IV. Rat dendritic cells present soluble and insoluble azobenzenearsonate conjugates to T cells

We have used a fractionation procedure involving bovine serum albumin gradient floatation, adherence to glass, and rosetting with antibody-coated sheep erythrocytes to purify an accessory cell fraction from Lewis rat spleens. The fraction which is of light buoyant density, nonadherent, and FcR- is markedly Ia+, lacks phagocytic ability, is nonspecific esterase negative and under scanning electron microscopy has a heterogeneous morphology with a variety of protuberences described for rat dendritic cells. This putative dendritic cell preparation is very effective at stimulating proliferative responses with concanavalin A and allogeneic cells. When used to reconstitute the reactivity of peritoneal exudate cells of rats immunized with azobenzenearsonate-N-acetyl-L-tyrosine (ABA-Tyr) and subsequently depleted of Ia+ cells, it was shown to be highly effective with ABA conjugates of tyrosine, Ficoll, and polystyrene beads. Thus, despite the apparent absence of phagocytic or degradative abilities, this cell was very efficient at presenting large soluble and insoluble antigens. It is suggested that processing may occur at the cell surface without requiring internalization.