1422 Acute Phase Reaction of Hamster Female Protein

Acute phase proteins are serum constituents that change in concentrat ion after injury. This acute phase reaction may result in decreased serum levels (albumin), or more frequently, a 50-300% increased serum level (Ca or haptoglobin) (1, 2). H u m a n C-reactive protein (CRP) x is the classic acute phase reactant , its level increas ingas much as 500-fold after injury (for review see reference 3). The beneficial effects of C R P in the inf lammatory response are unknown al though C R P can initiate or modulate a variety of biological events (4). Furthermore, C R P has evolved conservatively, insofar as homologous proteins with similar functional attributes have been found in m a n y other species: the stable preservation of this protein during evolution implies some biological importance (5). In general, C R P homologs are present at relatively low serum levels, and sex of the species has little influence on normal content or acute phase changes after injury. A serum protein homologous to C R P has been described in the Syrian hamster. This protein, called female protein (FP) (6), has structural and functional features in c o m m o n with C R P (7). However, FP is an unusual homolog because it is a prominent serum protein in females (1-2 mg/ml) , and because its expression is sex limited, normal males having low serum levels (6). In the present report, the capacity of FP to respond as an acute phase protein was examined in male and female Syrian hamsters. The results indicated a divergent sexlimited acute phase response, characterized by increased FP serum levels in males and a transient decrease in females. W h e n male / female FP levels were inversed by hormonal manipulat ion, a corresponding change in acute phase response also occurred, so that the pat tern of response was related to high or low serum FP concentrat ion rather than gender per se. Studies with 125I-FP indicated a similar catabolism of FP in both sexes under normal conditions and during acute phase changes; therefore, the variations in FP levels primarily reflect differences in rate of FP synthesis rather than degradation.