Isolation and Partial Characterization of an Antigen Associated with Pregnancy in the Ewe

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Abstract
A precipitating antiserum raised in calves against sheep embryonic membranes was rendered specific for an antigen associated with pregnancy by absorption with sheep liver and kidney tissue. The Ouchterlony gel precipitin test was used to monitor the purification of ovine pregnancy-associated antigen (oPAA) from homogenized embryonic membranes. The antigen exhibited properties similar to known glycoproteins during conventional chromatographic and electrophoretic procedures. The purified antigen appeared to exist in high and low molecular weight forms (42,600 and 17,400 daltons, respectively) and the data suggested that these represented dimeric and monomeric forms of the antigen. The properties of this antigen are compared with those of other pregnancy-associated substances and the possible biological importance of the antigen is discussed.