Cytokine-mediated human polymorphonuclear neutrophil phagocytosis: evidence of differential sensitivities to manipulation of intracellular mechanisms

Interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF-alpha) are well known mediators in infectious processes with pleiotropic effects on a variety of cells. These cytokines are known to upregulate Fc receptor (Fc gamma R)-mediated phagocytosis by human polymorphonuclear neutrophils (PMN) but the mechanisms of this enhanced phagocytosis are not known. We investigated the effects of various alterations in intra- and extracellular events on cytokine-induced phagocytic upregulation. Blockade of mRNA synthesis, protein kinase C activation, or G protein activation prevented enhanced phagocytosis by either cytokine. The PMN phagocytic response to TNF-alpha, but not IL-1 beta, was also blunted by agents interfering with mRNA translation or Fc gamma R recycling.

Immunogenic properties of Pseudomonas aeruginosa mucoid exopolysaccharide

Previous studies have shown that antibodies to Pseudomonas aeruginosa mucoid exopolysaccharide (MEP) can be divided into two types on the basis of their functional activity. One type is able to mediate opsonic killing in conjunction with leukocytes and complement, and the other type is not. We investigated, in mice, the properties of this antigen associated with elicitation of opsonic killing antibody. We found that smaller-sized material (Kav = 0.26), which has been tested as a human vaccine, elicited opsonic killing antibody in mice at low doses (1 to 10 micrograms) and at doses of greater than or equal to 40 micrograms, only nonopsonic killing antibody was produced. A similar dose effect was seen with heat-killed mucoid P. aeruginosa cells. After immunization with high doses of this MEP or the heat-killed cells, the mice were refractory to induction of opsonic killing antibody no matter what dose of MEP was used as a booster. In contrast, a larger-molecular-weight preparation (Kav = 0.05) elicited opsonic killing antibody over a wide dose range (1 to 400 micrograms). Additionally, 50 micrograms of the larger-sized preparation could overcome the suppression induced by 50 micrograms of the smaller material. Suppression elicited by 50 micrograms of the smaller material could be adoptively transferred to nonimmune mice with the T-cell fraction of spleen cells. These results indicate that both molecular size and dose are critical determinants for eliciting opsonic killing antibody to mucoid P. aeruginosa after immunizing with MEP.

Bacteremia with Streptococcus bovis and Streptococcus salivarius: clinical correlates of more accurate identification of isolates

Two biotypes of Streptococcus bovis can be identified by laboratory testing and can be distinguished from the phenotypically similar organism Streptococcus salivarius. We assessed the clinical relevance of careful identification of these organisms in 68 patients with streptococcal bacteremia caused by these similar species. S. bovis was more likely to be clinically significant when isolated from blood (89%) than was S. salivarius (23%). There was a striking association between S. bovis I bacteremia and underlying endocarditis (94%) compared with that of S. bovis II bacteremia (18%). Bacteremia with S. bovis I was also highly correlated with an underlying colonic neoplasm (71% of patients overall, 100% of those with thorough colonic examinations) compared with bacteremia due to S. bovis II or S. salivarius (17% overall, 25% of patients with thorough colonic examinations). We conclude that careful identification of streptococcal bacteremic isolates as S. bovis biotype I provides clinically important information and should be more widely applied.