Serum Factors and the Reticuloendothelial Uptake of Staphylococcus aureus II. Role of a Zymosan-Adsorbable Serum Opsonin

ABSTRACT

A heat-stable factor in the serum of normal rabbits adsorbed by zymosan at 16 C in the presence of ethylenediaminetetraacetic acid has been found to enhance the uptake of an encapsulated strain of Staphylococcus aureus (Smith diffuse) by the isolated perfused rabbit liver. This opsonin does not appear to be a rate-limiting component of the hemolytic complement system, properdin, immunoglobulins G or M. It does, however, require the presence of a heat-labile cofactor(s) for expression of its activity.