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A B S T R AIn the two instances studied, mothers of twins showed abnormally high PAPP levels.

Frozen sections of human placenta were examined for the presence of four human pregnancy proteins, pregnancy-associated plasma proteins A and C (PAPP-A and PAPP-C), human chorionic somatomammotropin (hCS), and pregnancy zone protein (PZP), by the indirect immunofluorescence technique. Monospecific rabbit antiserums to PAPP-A, PAPP-C and hCS all stained the trophoblast cytoplasm equivalently in a continuous layer, usggesting that the same trophoblast cells synthesize all three pregnancy proteins. In contrast, PZP was localized in blood vessel walls, parenchymal structures within the villous, as well as in the trophoblast cytoplasm. Its distribution in the latter was relatively inhomogeneous, tending to be more intense on the basement membrane side.

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In order to understand the pathogenesis of any infectious process, it is obviously necessary to have knowledge of the substances produced in the tissues by the micro-organisms which may play active roles in the disease. In the past, such substances have been detected by much effort, or by chance. When they have been discovered, evidence regarding the production of such materials in vivo during the infection has often been obtained by examining human patients for antibody response to these products. It has been pointed out previously (1-3) that the use of precipitin analysis in agar furnishes a valuable tool for estimating the total number of antibody responses which occur as a result of infection. This in turn, of course, reflects the total number of antigens or toxins secreted by the infecting agent in vivo. The use of human antibodies automatically restricts our studies to those antigens formed in vivo, and prevents diversion of interest to substances produced by the micro-organism in cultures alone. The use of these precipitin technics also furnishes the tool for following the isolation, purification, and eventual characterization of each of the antigens so detected. It is the purpose of the present report to describe the use of this approach for the separation and analysis of streptococcal antigens detected with human antibodies.Human sera have revealed a surprisingly large number of extracellular antigenic components to be present in a Group A streptococcal culture concentrate (1-3). Pooled gamma globulin samples from normal individuals were also very