The binding of the iC3b receptor (CR3) to unopsonized zymosan was shown to result from CR3 attachment to cell wall ß-glucans. A specificity of neutrophil responses for ß-glucan was first suggested by a comparison of yeast (Saccharomyces cerevisiae) cell wall components for stimulation of a neutrophil superoxide burst. Neutrophils responded poorly to heat-killed yeast, but gave increasingly better responses to cell wall polysaccharides devoid of proteins (zymosan) and nearly pure ß-glucan particles derived from zymosan. Zymosan triggered a burst that was 29% as great as that stimulated by phorbol myristate acetate (PMA), and ß-glucan particles stimulated a burst that was 72% as great as that produced by PMA. Phagocytic responses to yeast were also inhibited by soluble glucans but not by soluble mannans. Three types of experiments demonstrated a role for CR3 in these responses. First, neutrophil ingestion of either yeast or yeast-derived ß-glucan particles was blocked by monoclonal anti-CR3, fluid-phase iC3b, or soluble ß-glucan from barley. Monocyte ingestion of ß-glucan particles was also blocked by anti-CR3, but not by anti-CRi or anti-C3. Second, the neutrophil superoxide burst response to either zymosan or ß-glucan particles was blocked by anti-CR3 or fluid-phase iC3b, and was completely absent with neutrophils from 3 patients with an inherited deficiency of CR3. Third, CR3 was isolated from solubilized neutrophils by affinity chromatography on ß-glucan-Sepharose.

Previous studies have suggested that neutrophil complement receptor type three (CR3) has two binding sites: (1) a site for fixed iC3b that does not trigger ingestion or a superoxide (O2) burst, and (2) a function-triggering site for the ß-glucan component of yeast (Saccharomyces cerevisiae) cell walls. In the present study it was found that yeast (Y) coated with C3b (YC3b) or iC3b (YC3bi), prepared with purified complement in an IgG-free system, were avidly ingested and stimulated a vigorous O2 burst, whereas sheep erythrocytes (E) bearing C3b or iC3b, were not ingested and did not give an O2 burst. YC3b and YC3bi contained an amount of fixed C3 that was approximately equal to serum-opsonized Y (OY), and produced O2 bursts comparable to OY. Experiments utilizing rabbit F(ab')2 anticomplement receptor type one (anti-CRj) to block fixed C3b binding to CRj, and monoclonal anti-CR3 (MN-41 or OKM1) to block fixed iC3b and Y cell wall binding to CR3, indicated that the O2 burst response to OY was primarily due to fixed iC3b and Y cell wall binding to CR3. Fixed C3b (that represented 33% of the fixed C3 on OY) and IgG anti-Y antibodies that bound to CRi and Fc receptors, respectively, were found to contribute little to the response. Although YC3b did bind avidly to neutrophil CRi, the results suggested that the O2 burst response to YC3b was triggered after the initial YC3b binding by the secondary attachment of Y cell wall components to CR3. When neutrophils were treated with anti-CR3, 90% of neutrophils bound YC3b (via CRi), but phagocytosis and an O2 burst were completely absent. Similar findings were made with OKM1-treated neutrophils and YC3bi. Responses of OKM1-treated neutrophils were inhibited because only the iC3b-binding site of CR3 was ligated by the YC3bi. Thus, fixed C3b or iC3b on Y mediate avid binding of Y to neutrophils via CRi or the iC3b-binding site of CR3, respectively, but ingestion and an O2 burst response are only triggered when glucans in the Y cell wall secondarily bind to neutrophils via the ß-glucan binding site of CR3.

T cells are essential for controlling infection with

In type 1 diabetes mellitus (T1DM), T cell-mediated destruction of insulin-producing pancreatic β cells leads to the acute onset of hyperglycemia. The nonobese diabetic mouse model of human T1DM reveals that T cells capable of inducing diabetes can escape normal central tolerance, and can cause T1DM if left unchecked. However, several regulatory T cell subsets can temper autoaggressive T cells, although it remains undetermined when and how, and by which subset, homeostatic control of diabetogenic T cells is normally achieved in vivo. Using a cotransfer model, we find that NKT cells efficiently dampen the action of diabetogenic CD4+ T cells, and do so in an indirect manner by modifying the host environment. Moreover, the NKT cell-containing population modifies the host via production of IFN-γ that is necessary for driving the inhibition of diabetogenic T cells in vivo.

T cells can be divided into two groups on the basis of the expression of either ␣␤ or ␥␦ T-cell receptors (TCRs). Because the TCR ␦ chain locus lies within the larger TCR ␣ chain locus, control of the utilization of these two receptors is important in T-cell development, specifically for determination of T-cell type: rearrangement of the ␣ locus results in deletion of the ␦ coding segments and commitment to the ␣␤ lineage. In the developing thymus, a relative site-specific recombination occurs by which the TCR ␦ chain gene segments are deleted. This deletion removes all D␦, J␦, and C␦ genes and occurs on both alleles. This ␦ deletional mechanism is evolutionarily conserved between mice and humans. Transgenic mice which contain the human ␦ deleting elements and as much internal TCR ␦ chain coding sequence as possible without allowing the formation of a complete ␦ chain gene were developed. Several transgenic lines showing recombinations between deleting elements within the transgene were developed. These lines demonstrate that utilization of the ␦ deleting elements occurs in ␣␤ T cells of the spleen and thymus. These recombinations are rare in the ␥␦ population, indicating that the machinery for utilization of ␦ deleting elements is functional in ␣␤ T cells but absent in ␥␦ T cells. Furthermore, a discrete population of early thymocytes containing ␦ deleting element recombinations but not V␣-to-J␣ rearrangements has been identified. These data are consistent with a model in which ␦ deletion contributes to the implementation of a signal by which the TCR ␣ chain locus is rearranged and expressed and thus becomes an ␣␤ T cell.Peripheral T cells can be divided into two groups on the basis of the heterodimeric antigen receptor displayed on the surface of the cell. Most mature T cells have ␣ and ␤ chains paired with CD3, while T-cell receptor (TCR) ␥ and ␦ chains are associated with CD3 on quite different T cells (1,5,10,21,32,38). These two types of T cells have different tissue distributions and appear to have different functions (2,4,43).While heavy and light immunoglobulin chains, as well as TCR ␤ and ␥ chains, have distinct chromosomal localizations (30, 31), the TCR ␦ chain locus is contained within the much larger TCR ␣ chain locus on chromosome 14 in both mice and humans (9,22,24,36,45,49). This unique organization of TCR loci poses interesting questions concerning the use of these distinct receptor chains. TCR ␣ and ␦ chains never appear on the same cell, implying exclusivity. Aside from a few variable (V) regions which can be found in ␣ or ␦ chains, there is no mixing of the elements between these genes (8, 15). There must exist mechanisms that prevent incorporation of internal ␦ chain segments in ␣ chains and that inhibit TCR ␣ chain rearrangement in ␥␦ T cells.A novel rearrangement observed in early thymocytes might implement the choice between becoming an ␣␤ T cell and becoming a ␥␦ T cell. This step involves deletion of the ␦ locus in cells destined to become ␣␤-bearing T cells. Two elements flanking the ...