A new procedure for analysing the relationship between different cell surface antigens

Monoclonal antibodies which identify carbohydrate-defined MHC class I epitopes

Eleven different monoclonal antibodies specific for H-2K- and H-2D-encoded Class I molecules have been screened to determine Class I epitopes dependent on both carbohydrate and protein structures. Monoclonal antibodies have been identified which bind to carbohydrate-defined antigens encoded by both the H-2K and H-2D gene regions. Sensitivity to glycosidases versus pronase has been used to classify antigens both expressed as cell surface molecules and when prepared as detergent solubilized antigen. Several simple sugars have also been found to act as inhibitors of antibodies which bind to carbohydrate-defined sites. The genetic control of carbohydrate antigen expression by H-2K- and H-2D-linked genes has been verified since a specific antibody does not bind to H-2Kb or H-2Db molecules encoded by several mutant strains of mice containing single amino acid substitutions in their protein product. All of these data are consistent with Class I antigenic structures being encoded in carbohydrate as well as protein moieties.

Identification of class I H-2Db molecules primarily expressed by B lymphocytes in murine spleen

Evidence is presented which supports the phenomenon of heterogeneity amongst H-2Db-encoded Class I molecules. Two monoclonal antibodies (MoAb) called H141-31 and B22-249 were used in these studies. Both bind to the 'private' H-2.2 site of H-2Db-encoded molecules, but the binding of B22-249 is determined by carbohydrate moieties, whereas H141-31 appears to bind to a protein-defined epitope. Some H-2Db molecules, identified by the H141-31 MoAb, are primarily expressed on B lymphocytes and not T lymphocytes in spleen. The number of H-2Db molecules which bind H141-31 on B cells was also found to be three- to four-fold less than the number which bound the B22-249 MoAb. B cells of two mutant strains of mice, B6-C.H-2bm13 and B6-C.H-2bm14 which harbour very few nucleotide changes in the H-2Db gene, also show marked reduction in the binding of both antibodies. This suggests that a single common gene encodes both target molecules and that post-translational modifications such as differential glycosylation may account for heterogeneity amongst H-2Db molecules. This would explain the presence of the different H-2Db molecules defined here. It follows that differences in glycosylation evidently occur both within the B cell population, since H141-31 binds to only a subset of H-2Db molecules on B cells, and between T and B lymphocytes, since resting T cells do not bind H141-31 MoAb.

Fractionation of detergent lysates of cells by ammonium sulphate-induced phase separation

A procedure is described for fractionating detergent lysates of cells based on the ability of (NH4)2SO4 to induce phase separation of detergents such as Triton X-100, sodium deoxycholate, and sodium cholate, into detergent-rich and detergent-depleted phases. An analysis of six murine lymphocyte cell surface molecules revealed that the partitioning in Triton X-100 of each molecule was highly dependent upon the (NH4)2SO4 concentration, each antigen partitioning into the detergent-rich phase at a defined salt concentration. In contrast, none of the six molecules appeared in the detergent-rich phase of a Triton X-114 phase separation, even though two of the molecules, namely Ly-2/3 and L3T4, are well-characterized integral membrane proteins. It was also observed that (NH4)2SO4 resulted in the partitioning of many nonmembrane proteins into the detergent-rich phase, indicating that the procedure can be used to fractionate all cellular proteins. By judicious choice of (NH4)2SO4 concentrations, precipitation of cellular proteins at two different (NH4)2SO4 concentrations, and combining the method with subcellular fractionation prior to detergent solubilization, substantial enrichment and concentration of particular cellular proteins could be achieved.

A rapid, automated colorimetric assay for measuring antibody binding to cell surface antigens

An automated, colorimetric procedure is described for detecting antibodies specific for cell surface antigens. The procedure entails (a) coating the wells of 96-well microplates with either protein A or anti-immunoglobulin antibodies and (b) preincubating either the microplate or target cells with the test antibody. Target cells which react with the test antibody bind to the wells of the microplate and bound cells are quantitated by staining with the dye Rose Bengal. A microplate spectrophotometer is used to measure absorbance in each well of the plate, providing a rapid, automated measure of antibody titre. The assay is simple to perform, uses readily available reagents and gives comparable sensitivity to rosetting assays. With these features, and the capacity for handling large numbers of trays quickly, this method has obvious advantages in screening for antibody activity in culture supernatants of hybridoma clones.

The definition of an MB related specificity by a monoclonal antibody

A number of monoclonal antibodies have been described that react with monomorphic and polymorphic Ia-like specificities on human B cells, but it is not clear whether these react with HLA-DR encoded molecules or with the products of other closely linked genes within the MHC, such as MB, MT, or DC 1 antigens. A monoclonal antibody is described herein (MC-26.1) which detects a new Ia-like specificity as shown by B-cell reactivity, chemistry, family studies, including recombinant family and coprecipitation studies. The latter studies showed that specificity detected by the MC-26.1 antibody coprecipitated with determinants detected by conventional anti-MB3 and MT3, but not with HLA-DR4 antisera. The determinant was polymorphic but not related to any of the known MB or MT specificities. However, cross-reactions were demonstrated by the variability of reaction on different individuals. Coprecipitation studies indicate that the antigen defined by MC-26.1 coprecipitates with MB and MT specificities suggesting that the antibody defines a new specificity on the MB3 and MT3 molecules.

Automated rosetting assay for cell surface antigens and autorosetting lymphocytes

An automated procedure, using a Coulter counter, is described for enumerating rosette-forming lymphocytes in 2 rosetting systems in mice, detecting antibodies to cell surface antigens, and the interaction of autologous erythrocytes with thymocytes (autorosetting). The procedure gives results comparable with determinations of rosettes by light microscopy. The procedure not only estimates rosetting percentages, but can be used to titrate anti-lymphocyte antibodies, to detect autorosette inhibition factor in serum and to assay cell surface antigens in detergent lysates of spleen cells.

A sensitive and quantitative fluorescence assay for cell surface antigens

A procedure is described for the assay of cell surface antigens based on quantitative fluorometry. Fluorescent immunospheres are coupled with sheep anti-mouse immunoglobulins or Protein A and used to detect specific antibody bound to target cells. The fluorescent sphere assay described here offers 16--128-fold greater sensitivity than complement mediated lysis or Protein A radioimmune assays and comparable sensitivity to rosetting assays. In addition, the assay is simple to perform, uses commercially available reagents and is completely objective in that a common laboratory fluorometer is used to obtain fluorescence measurements.

H-2U: a new region at the D end of the murine MHC

A new genetic region, mapping within the H-2 complex, has been serologically defined with several alloantisera raised in mice which differ at the D region. When these antisera were absorbed to remove H-2D antibodies, residual antibody activity remained that reacted in a strain-specific manner, and the antigens involved mapped to a new genetic region between the S and D regions. Two allelic variants relating to the d and k haplotypes have been defined by genetic mapping studies. This new region has been designated H-2U and the antigens it controls appear to resemble Ia antigens in their cellular distribution and molecular weight. The new antigen is primarily expressed on B cells, and is carried on protein molecules having approximate molecular weights of 36 000 and 60 000 daltons and resembling the alpha and alpha--beta chain dimer characteristic of Ia antigens.