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One of six monoclonal antibodies raised against purified human placental alkaline phosphatase cross-reacts with the adult and fetal forms of intestinal alkaline phosphatase. The placental and intestinal enzymes are nonallelic. A new electrophoretic titration procedure was used to assess the relative reactivities of the different enzymes with the antibody. The placental enzyme was the most reactive. However, the adult intestinal enzyme showed greater reactivity than the fetal enzyme. The determinants to which the antibody binds on these three forms of alkaline phosphatase presumably differ in their detailed molecular configurations.

Enzyme-monoclonal antibody complexes formed between six different monoclonal antibodies and the six phenotypes of human placental alkaline phosphatase [orthophosphoricmonoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] that represent the homozygous and heterozygous combinations of the three common alleles have been examined by electrophoresis in starch, acrylamide, and agarose gels. Since the complexes formed retain full enzyme activity, they could be detected after gel electrophoresis by an enzyme stain. Distinctive electrophoretic patterns were obtained with each monoclonal antibody. Differential binding of certain of the antibodies with the products of different alleles produces clear discrimination of various homozygous and heterozygous phenotypes. This discrimination parallels the results previously obtained by using a quantitative binding radioimmunoassay. The results show that this general method should prove useful in screening hybridoma fluids for the presence of monoclonal antibodies to specific enzymes; in the detection of allelic variation, even where this is not expressed by electrophoretic differences among the uncomplexed enzymes; and in discriminating between homozygotes and heterozygotes. It could also prove to be a useful tool in the elucidation of the molecular structures of enzyme-monoclonal antibody complexes.

No abstract

Almost all human leukocyte antigen (HLA) haplotypes positive for HLA-DR4 also carry the DQw3 specificity, which appears in one of two allelic forms, DQw3.1 or DQw3.2. Previous studies have shown that the frequency of the HLA DR4-DQw3.2 allele is approximately 95% among DR4-positive haplotypes of insulin-dependent diabetics (IDDM), but only 70% in DR4-positive haplotypes of unaffected individuals. Because this difference could be due to ethnic heterogeneity, it is important to establish whether the frequency of the DQw3.2 allele is also increased when haplotypes of diabetics are compared to those of "matched" unaffected individuals, as can be done within families. We have used the Genetic Analysis Workshop 5 (GAW5) data for this purpose. In every family, each parental DR4-bearing haplotype was categorized as "IDDM" if it appeared in any affected parent or offspring, or as "control" if not. When this was done, the frequencies of the DQw3.2 and 3.1 allele in 80 IDDM haplotypes were 94% and 6% respectively but 67% and 33% in 15 control haplotypes. This difference between the two kinds of haplotypes is highly significant (P less than 0.005).