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The capability of macrophages to inactivate ingested staphylococci can be augmented when repeated infection is followed by specific elicitation with staphylococcal lysate. The increase in staphylococcidal capability with specific elicitation after infection is not dramatic but is statistically significant. The percentage of change in staphylococcidal capability after infection and specific elicitation is systematically related to the staphylococcidal capability of the populations of macrophages in the same rabbits studied prior to infection. When the capability of the initial populations of macrophages has been high, the percentage of change after infection and elicitation may be slight or even negative. When the staphylococcidal capability of the initial population of macrophages in a given rabbit has been low, there is typically a significant increase in this capability after infection and elicitation. It is shown at the cellular level that it is possible to evoke a population of activated macrophages, by a procedure which is analogous to procedures reported as useful in human practice.

The staphylococcidal capability of populations of peritoneal macrophages in rabbits has been measured before and after repeated infections with Staphylococcus aureus. Such rabbits after infection showed delayed-type hypersensitivity to S. aureus antigens, but the staphylococcidal capability of the peritoneal macrophages was not increased. This result at the cellular level is in agreement with previous assessment in vivo of the consequences of staphylococcal infection. Pathways to cell-mediated resistance, with and without delayed-type hypersensitivity, are presented.

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Summary A protein agglutinogen common to the internationally recognized serotypes of Staphylococcus aureus is described. Sera of all human subjects studied, healthy or infected, possess a high and fairly uniform level of antibodies against this agglutinogen. The agglutinin is concentrated in commercial human γ-globulin and is deficient in the blood of agammaglobulinemic children. No immunizing agent has been found which will regularly increase agglutination titers in man to a significant degree, although some increase has been induced in rabbits. Serum absorbed with the pure protein agglutinogen shows decreased agglutination titer against all serotypes but is not deprived of its phagocytosis promoting power.