A large proportion of sickle erythrocytes is removed from the circulation by the macrophages of the reticuloendothelial system. In view of the proposed role for natural antibodies in the destruction of normal senescent erythrocytes, we looked for a possible similarity in the antibodies that bind in situ to senescent and sickle cells. Bound IgG molecules were detected by a highly sensitive rosetting antiglobulin test, using K562 myeloid cells. After separation on Stractan density gradients, the 0.6% most dense (senescent) normal cells and the most dense 40% sickle cells displayed membrane-bound IgG as reflected by the high proportion of rosettes formed. No antibody was found on low-density cells of either type. The bound antibodies were readily eluted from both sickle and normal senescent cells by carbohydrates containing alpha-galactosyl residues. These antibodies appear identical to the recently discovered human natural anti-alpha-galactosyl IgG (anti-Gal), an IgG antibody present in high titers in normal sera. Moreover, affinity-purified anti-Gal interacted specifically with sickle and normal cells depleted of the autologous antibodies. A similar pattern of binding to the various erythrocyte subpopulations was observed when the radiolabeled lectin with anti-alpha-galactosyl specificity, Bandeiraea simplicifolia, was used. In vitro phagocytosis of normal and sickle erythrocyte subpopulations correlated with the presence of anti-Gal on these cells. The in situ binding of anti-Gal to a large proportion of sickle erythrocytes may reflect an accelerated physiologic aging process by which immune recognition of prematurely exposed alpha-galactosyl-bearing antigenic sites contributes to shortened cell survival.

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Excessive binding of natural anti-alpha-galactosyl immunoglobin G to sickle erythrocytes may contribute to extravascular cell destruction.

A sensitive radioimmunoassay and an antibody class-specific enzyme-linked immunosorbent assay were used to determine whether patients cured of cryptococcosis responded normally to immunization with cryptococcal capsular polysaccharide (CPS) and type III pneumococcal polysaccharide. 10 normal volunteers and 8 patients who had been cured of cryptococcal meningitis and who had been cured of cryptococcal meningitis and who had no serious underlying diseases were immunized with both antigens. Geometric mean titers to CPS measured by radioimmunoassay were 1:1 in both groups before vaccination, but were 1:3 in patients and 1:119 in controls following immunization (P less than 0.01, Student's t test). Analysis of the class-specific response to immunization with CPS found little anti-CPS IgG or IgA. Geometric mean postvaccination IgM titers were 1:31 in patients and 1:238 in controls (P less than 0.01). Responses to immunization with type III pneumococcal polysaccharide were similar in patients and controls, with IgA, IgM, and IgG mean titers of 1:1129, 1:369, and 1:158 in patients and 1:1504, 1:1039, and 1:163 in controls (P greater than 0.2 for each antibody class). Cured cryptococcal meningitis is often associated with prolonged specific immunologic unresponsiveness.

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Long-lasting, specific immunologic unresponsiveness associated with cryptococcal meningitis.

Antibodies produced by an individual without a known history of sensitization to the relevant antigen are called "natural" antibodies. Some natural antibodies, called xenoreactive antibodies, react with the cells of foreign species. Most xenoreactive antibodies in humans and higher primates bind to a nonreducing terminal galactose expressed by pigs and other lower mammals. Although human natural antibodies which bind to one or more of a variety of terminal alpha-galactosyl structures have been identified previously, the antigen recognized by anti-alpha-galactosyl antibodies on the cells of foreign species is thought to be exclusively Galalpha1-3Gal. Thus, anti-alpha-galactosyl antibodies which do not react with Galalpha1-3Gal are thought to be nonxenoreactive. Here, we identify natural antibodies in human serum which bind to Galalpha1-6Hexosepyrranosides but not Galalpha1-3Gal, indicating that these antibodies are not xenoreactive. Various lower mammals were found to have natural anti-Galalpha1-2Gal antibodies in their sera, suggesting that at least some anti-Galalpha1-2Gal antibodies might not be xenoreactive and indicating, surprisingly, that anti-alpha-galactosyl antibodies are much more phylogenetically disperse than previously known. Also surprising was the finding that some natural antibodies which bind to Galalpha1-3Gal in vitro do not bind to porcine xenografts. These studies show that naturally occurring anti-alpha-galactosyl antibodies in mammalian serum include antibodies with a greater variety of reactivities than previously thought, only some of which would bind to a porcine xenograft. Further, these studies show that the methods used to detect anti-alpha-galactosyl antibodies of relevance in xenotransplantation must be carefully evaluated to avoid detection of anti-alpha-galactosyl antibodies which would not bind to a porcine organ and which therefore are not involved in xenograft rejection.

/pdf/naturally-occurring-anti-a-galactosyl-antibodies-2w8hxl18tr.pdf

Naturally occurring anti-α-galactosyl antibodies: Relationship to xenoreactive anti-α-galactosyl antibodies

A glucose-dependent hemagglutinin, present in the serum of an apparently healthy donor, is shown to be a polyclonal IgM immunoglobulin with specificity for beta-D-glucopyranose configuration. The antibody did not agglutinate erythrocytes coated with hexoses differing from glucose at C2, C3, or C4 positions or lacking the primary alcohol group at C6 position. The hemagglutination reaction, quantitated in a continuous flow system, was inhibited by the addition of 6-deoxyglucose, 5-thioglucose, 2-deoxyglucose, 2-aminoglucose or 3-0 methylglucose. D-glucose, in beta- but not in alpha-configuration, attached by a glycosidic bond to another glucose or to an aglycone, was also inhibitory. A cross-reactivity was demonstrated between glucose and 6-deoxyglucose by antibody absorption and elution techniques. The donor's serum contained independent antibodies that reacted with erythrocytes coated with melibiose, gentiobiose, cellobiose, or N-acetylmannosamine. Further investigation revealed that antibodies are present in sera of all normal adults against erythrocytes coated with melibiose and N-acetylmannosamine and with high frequency against erythrocytes coated with gentiobiose, L-rhamnose, cellobiose, D-mannose, lactose, or D-galactose.

Carbohydrate‐Specific Antibodies in Normal Human Sera

Lactosylsphingosine-reactive antibody and CEA in patients with colorectal cancer

Human sera were screened by passive haemagglutination for antibodies to various sugars. A high incidence of antibodies to melibiose was observed. There were also a few antibodies to other sugars and to dextran.

G. W. G. Bird

Papers

Human serum antibodies to melibiose and other carbohydrates.