Inhibition of secondary IgG responses by N-acetyl-D-galactosamine

Surface carbohydrate composition of a tapeworm in its consecutive intermediate hosts: Individual variation and fitness consequences

Carbohydrates on parasite surfaces have been shown to play an important role in host-parasite coevolution, mediating host non-self recognition and parasite camouflage. Parasites that switch hosts can change their surface molecules to remain undetected by the diverse immune systems of their different hosts. However, the question of individual variation in surface sugar composition and its relation to infectivity, virulence, immune evasion and growth of a parasite in its different hosts is as yet largely unexplored. We studied such fitness consequences of variation in surface sugars in a sympatric host-parasite system consisting of the cestode Schistocephalus solidus and its intermediate hosts, a copepod and the three-spined stickleback. Using lectins to analyse the sugar composition, we show that the tapeworm changes its surface according to the invertebrate or vertebrate host. Importantly, sugar composition seems to be genetically variable, as shown by differences among tapeworm sibships. These differences are related to variation in parasite fitness in its second intermediate host, i.e. infectivity and growth. Surface sugar composition may thus be a proximate correlate of the evolutionarily relevant variability in infectivity and virulence of parasites in different hosts.

Modulation of the secondary antibody response of murine lymphocytes to sheep red blood cells in vitro by neuraminidase and exoglycosidases

The effect of digestion of lymphocytes with neuraminidase and exoglycosidases on the secondary antibody response in vitro to sheep red blood cell (SRBC) antigen was tested. Treatment of spleen cells from SRBC-primed mice with 3 micrograms/ml of neuraminidase slightly but significantly augmented their plaque-forming cell response to SRBC, whereas treatment with 100 micrograms/ml of a mixture of exoglycosidases did not. Rather unexpectedly, however, treatment of the spleen cells with the mixture of both neuraminidase and exoglycosidases greatly augmented the response. This enzyme action was substrate specific inasmuch it was ablated by addition of mucin as a neuraminidase inhibitor to the enzyme mixture. The target of the enzyme activity was not glass-adherent macrophages, but was glass-non-adherent suppressor cells in the antigen-primed cell population. Evidence was provided that the phenotype of suppressor cells whose activity was ablated by the enzyme treatment was Thy-1+. It is suggested from these results that sialylated complex type oligosaccharides on antigen-primed T cells play a critical role in their suppressor activity.

Anti-immunoglobulin M induces both B-lymphocyte proliferation and differentiation in Xenopus laevis

Anti-IgM induced the proliferation of spleen lymphocytes of the amphibian Xenopus laevis as determined by 3H-thymidine uptake. The responding cells were B lymphocytes, since lymphocyte populations enriched in surface-Ig-positive cells exhibited an increased proliferative response, and spleen cells from larvally thymectomized animals still responded to anti-IgM. Immunofluorescence analysis and gel electrophoresis of biosynthetically labeled Ig polypeptides revealed that lymphoblasts induced by anti-IgM differentiated into plasmablasts that synthesized and secreted mainly IgM and small amounts of IgY. The in vitro differentiation of B lymphocytes also occurred in spleen cells obtained from thymectomized animals. These findings are in contrast with those obtained in mammals and suggest that the differentiation of B lymphocytes in X. laevis is subject to different regulatory mechanisms.

In vitro generation of human activated lymphocyte killer cells. II. N-acetyl-D-galactosamine inhibits a distinct subpopulation of human activated lymphocyte killer cells generated in mixed lymphocyte culture

A range of monosaccharides was tested for its ability to inhibit the generation of cytotoxic cells during mixed lymphocyte culture. The most discriminatory effect was produced by N-acetyl-D-galactosamine (NADG). The presence of this sugar at the initiation of the coculture significantly inhibited in a dose-dependent manner the induction of a subset of nonspecific activated lymphocyte (ALK) cells preferentially able to lyse the K562 target cell (natural killer, NK-like cells) but had no effect on the generation of either specific cytotoxic T lymphocytes or another separate subset of ALK cells mediating lysis of an NK-insensitive melanoma cell line. The addition of conditioned medium containing interleukin 2 and interferon (IFN) at the start of culture reversed the inhibitory effect of the sugar. Under conditions of limiting dilution, the frequency of NK-like precursors ranged from 1/50 to 1/1200 with different mononuclear cells (MNC) and in all cases the presence of NADG from Day 0 of culture selectively decreased the frequency of these precursors. At the concentrations used NADG had no effect on NK-like cell cytolysis once generated. The addition of recombinant gamma-IFN did not abrogate the inhibitory effect of NADG and in MLC of some individuals decreased the frequencies of ALK cell precursors. These data provide further evidence for the heterogeneity of ALK cells and indicate that what is usually referred to as NK-like cell activity in in vitro culture is mediated by a subpopulation of MNC which are activated and induced to differentiate along a pathway independent of that of other ALK subsets.

Mouse serum as a medium supplement for murine immune responses in vitro

In vitro generation of secondary anti-viral H-2 restricted cytotoxic T cells (Tc cells) alloreactive Tc cells, alloantigen-induced T cell proliferation, bacterial lipopolysaccharide (LPS)-induced B cell proliferation and anti-dinitrophenyl IgM and IgG antibody responses were used to evaluate pools of mouse sera (MS) and other animal sera as medium supplements by comparison with 5-10% fetal calf serum (FCS). Some batches of normal MS were comparable with FCS while others inhibited Tc cell responses when used at 1%, particularly with limiting stimulator cell numbers. In contrast, 2 pools of nude mouse sera and several pools of MS from thioglycollate-injected mice (TMS) used at 1% were consistently comparable with FCS at 5-10% in terms of in vitro generation of effector Tc cells and antibody secreting B cells. TMS at 1% was satisfactory for Tc cell responses either fresh, after heat inactivation at 56 degrees C for 30 min, or after storage for 6 months at -70 degrees C. 0.5% or 2% heat-inactivated rat and rabbit sera (but not guinea pig sera) were also satisfactory for Tc cell generation. Total thymidine incorporation into proliferating B or T cells was 5-15-fold lower in cultures with 1% normal MS, nude MS or TMS than with 5% FCS, but stimulation indices with 1% nude MS and TMS were similar to those with 5% FCS, whereas 1% normal MS apparently completely inhibited stimulation. One percent syngeneic TMS is a convenient, reliable alternative to 5-10% FCS in culture medium, supporting all the murine responses listed above.

The immunomodulatory effect of anti-Micrococcus luteus antibodies. I. Effect on in vitro rabbit T cell functions

A range of purified rabbit anti-Micrococcus luteus antibodies (anti-MCAb) were tested for their ability to interfere with a variety of in vitro immune responses. Such antibodies strongly inhibited the secondary IgG antibody response to sheep red blood cells without affecting the IgM response or the proliferative responses to mitogens and antigens. By exposing lymphocyte populations to anti-MCAb, it was found that such reagents exerted a strong mitogenic effect on rabbit T lymphocytes, provided these cells were derived from antigen-activated lymph nodes. This mitogenic effect was also obtained with F(ab')2 fragments of anti-MCAb and with hybridoma-derived anti-MCAb. Collectively, these data indicate that anti-MCAb inhibit the initiation of IgG synthesis possibly through the expansion of immunoregulatory T cell subsets.

Selective inhibition by monosaccharides of tumor cell cytotoxicity mediated by mouse macrophages, macrophage-like cell lines, and natural killer cells

A series of monosaccharides were tested for their ability to inhibit the effector phase of macrophage-mediated cytolysis against two susceptible murine tumor target cells, L5178Y and RL male I. Two monosaccharides, D-mannose and N-acetyl-D-galactosamine, were found to decrease cytotoxicity consistently in a dose-dependent manner. However, D-mannose preferentially inhibited lysis of RL male I target cells with little effect on lysis of L5178Y target cells, while the reverse was found with N-acetyl-D-galactosamine. Neither monosaccharide interfered with the activation of macrophages by polyinosinic:polycytidylic acid. Natural killer cell activity was decreased by a 25 mM concentration of D-mannose but not by N-acetyl-D-galactosamine, although increasing concentrations of N-acetyl-D-galactosamine were inhibitory. Neither monosaccharide affected cytotoxicity by alloimmune T cells. Cytotoxicity of macrophage-like cell lines against tumor target cells was also decreased by monosaccharides but the pattern of inhibition was different from that seen with activated macrophage effector cells. Both D-mannose and N-acetyl-D-galactosamine inhibited glucose oxidation by activated macrophages but only D-mannose significantly decreased protein synthesis of activated macrophages. These results indicate that monosaccharides can inhibit macrophage-mediated cytotoxicity in a selective manner with the pattern dependent on the tumor target cell used in the assay.

Inhibition of secondary IgG responses by monosaccharides: evidence for I-region control

Certain monosaccharides selectively inhibit secondary IgG responses in vitro. Genetic analyses described in this report revealed that the inhibitory sugars differed between mouse strains and these differences mapped to the I-J and I-C subregions of the murine MHC. These results imply that interaction between T and B lymphocytes can involve the recognition of I-region controlled carbohydrate structures.