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In contrast to its macrophage-activating capacity, IFN-gamma downregulates expression of the macrophage mannose receptor (MMR), which mediates uptake of Candida and other microorganisms. We found that IFN-gamma induced a concentration-dependent increase in the capacity of human monocyte-derived macrophages to ingest and kill both opsonized and unopsonized Candida albicans and to release superoxide anion upon stimulation with Candida. Mannan or mannosylated albumin inhibited this activated uptake of unopsonized Candida, but glucan did not. Addition of mAb to complement receptor (CR) 3 did not inhibit ingestion; macrophages that lacked CR3 (leukocyte adhesion defect) showed normal upregulation of ingestion by IFN-gamma. The increased candidacidal activity of IFN-gamma-activated macrophages was associated with reduced expression of MMR by a mean of 79% and decreased pinocytic uptake of 125I-mannosylated BSA by 73%; K(uptake) of pinocytosis was not changed. Exposure of resident macrophages to unopsonized Candida did not elicit a transient increase in intracellular free Ca2+ ([Ca2+]i); macrophages activated by IFN-gamma expressed a brisk increase in [Ca2+]i on exposure to Candida. These data suggest that macrophage activation by IFN-gamma can enhance resistance to C. albicans infection in spite of downregulation of the MMR, perhaps through enhanced coupling of the MMR to microbicidal functions.

The Sézary syndrome is a frequently lethal disease characterized by circulating malignant cells of thymus-derived (T)-cell origin. The capacity of circulating malignant lymphocytes from patients with this syndrome to synthesize immunoglobulins and to function as helper or suppressor cells regulating immunoglobulin synthesis by bone marrow-derived (B) lymphocytes was determined. Peripheral blood lymphocytes from normal individuals had geometric mean immunoglobulin synthetic rates of 4,910 ng for IgM, 1,270 ng for IgA, and 1,625 ng for IgG per 2 X 10(6) cells in culture with pokeweed mitogen for 7 days. Purified normal B cells had geometric mean synthetic rates of 198 ng for IgM, 145 ng for IgA, and 102 ng for IgG. Leukemic cells from patients with the Sézary syndrome produced essentially no immunoglobulins. Adding normal T cells to normal B cells restored their immunoglobin producing capacity. Leukemic cells from four of five patients tested had a similar capacity to help immunoglobulin synthesis by purified normal B cells. Additionally, Sézary cells from one patient studied induced a nearly 10-fold increase in IgA synthesis by lymphocytes from a child with ataxia telangiectasia and selective IgA deficiency. Furthermore, these Sézary cells induced more than a 500-fold increase in IgG and IgA synthesis by lymphocytes from a child with Nezelof's syndrome. When Sézary cells were added to normal unfractionated lymphocytes, they did not suppress immunoglobulin biosynthesis. In addition, unlike the situation observed when large numbers of normal T cells were added to purified B cells, there was no depression of immunoglobulin synthesis at very high malignant T-cell to B-cell ratios. These data support the view that Sézary T cells do not express suppressor cell activity. The results presented in this paper suggest that neoplastic lymphocytes from the majority of patients with the Sézary syndrome originate from a subset of T cells programmed exclusively for helper-like interactions with B cells in their production of immunoglobulin molecules.

Elucidation of mechanisms involved in the control of colonic production of mucus requires direct examination of glycoprotein synthesis and secretion by colonic mucosa. In the past, the limited viability of intestinal mucosa in vitro has hampered such investigations. When maintained in an organ culture system, mucosal biopsies of rabbit colon and human rectum remained viable for 24 h as documented by morphologic appearance and a steady rate of protein synthesis and secretion. These biopsies also incorporated (14)C-labeled glucosamine into tissue glycoproteins and secreted labeled glycoproteins at a steady rate for 24 h. Glucosamine was predominantly incorporated into macromolecules that were ultimately secreted, in contrast to leucine, which was predominantly incorporated into tissue macromolecules. When studied by autoradiography, cultured rabbit colonic biopsies synthesized and secreted glycoproteins in vitro at cellular sites and over a time-course similar to those previously described for the intestine of intact animals. Acetylcholine consistently stimulated secretion of labeled glycoproteins but did not alter glycoprotein synthesis. In contrast, cycloheximide inhibited glycoprotein synthesis but had no effect on the secretion of newly synthesized glycoproteins. Rectal biopsies from patients with active ulcerative colitis incorporated increased amounts of [(14)C]glucosamine into glycoproteins during organ culture and secreted labeled glycoproteins more rapidly into the incubation medium when compared to biopsies obtained from healthy volunteers These findings indicate that organ culture provides a useful means of directly examining the synthesis and secretion of glycoproteins by healthy and diseased colonic mucosa.

The state of activation of normal human intestinal mononuclear cells obtained from transplant donors was studied. Compared with PBMC, freshly isolated intestinal mononuclear cells expressed significantly more cell surface activation antigens on both B and T lymphocytes. Intestinal mononuclear cells contained significant numbers of immunoglobulin secreting cells immediately after cell separation. This population included CD5-positive B cells that secreted predominantly IgA. Cells from the large bowel consistently revealed higher numbers of IgA secreting cells than cells from the small bowel. Thus, intestinal B cells are markedly activated in vivo compared with PBMC and this increased activation correlates with increased spontaneous antibody secretion. B cells from the large intestine are more highly activated and secrete more antibody than do cells from the small intestine. The intestinal lamina propria lymphoid compartment exhibits a heightened state of activation that may be important for its distinct role in mucosal defense.

We have compared the abilities of immunoglobulin (Ig)G, IgM, and IgA to induce either mononuclear cell-mediated (complement-independent) or complement-mediated (cell-free) antibacterial activity against group C meningococci. In each of these assays, immunoglobulins purified from the sera of individuals immunized with meningococcal group C polysaccharide were compared with those purified from sera of patients convalescing from disseminated meningococcal disease. Our data support three conclusions. First, although nonbactericidal in cooperation with complement, IgA can induce cell-mediated antibacterial activity as well as IgG. Second, the amount of IgG required to induce cell-mediated antibacterial activity is similar to the amount required for complement-mediated killing. Third, although the amount of either postimmunization or convalescent IgM required to induce complement-mediated killing is 16- to 20-fold less than the amount of respective IgG required, IgM is inferior to IgG in its ability to induce cell-mediated antibacterial activity because in the cell-mediated system (a) postimmunization IgM is ineffective; (b) the amount of convalescent IgM required for minimal activity is eightfold more than the amount of convalescent IgG required; and (c) the maximal antibacterial index induced by convalescent IgM is 50% less than that which can be induced by IgG. These data suggest that IgG and IgA may play a greater role than IgM in mononuclear cell-mediated antibacterial host immune defense.