Phagocytosis, chemoluminescence, and intracellular killing of fungi by phagocytes from subjects with deficiency of the second component of complement

Production and function of cytokines in natural and acquired immunity to Candida albicans infection

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.

Intracellular survival of Candida albicans in peritoneal macrophages from chronic peritoneal dialysis patients

Candidal peritonitis is a tenacious infection in patients undergoing chronic peritoneal dialysis. Since little is known about host defenses of the human peritoneal cavity against fungi, we investigated the interaction of peritoneal macrophages (PM phi) from uninfected dialysis patients with Candida albicans blastospores. Chemiluminescence (CL) techniques were used to assess the respiratory burst activity of these cells, and candidacidal activity was evaluated with a fluorochrome microassay. In sharp contrast to peripheral blood polymorphonuclear leukocytes (PMNs) from healthy donors, which gave a brisk luminol-enhanced CL response to opsonized blastospores and killed 35% of cell-associated organisms, PM phi produced barely detectable luminol-enhanced CL and killed only 13% of intracellular Candida. These findings appeared to be associated with a decreased level of myeloperoxidase in PM phi. The mechanism of intracellular survival of C albicans also appeared to be related to relatively poor triggering of superoxide production during phagocytosis of viable blastospores. The CL response of PMNs to C albicans was opsonin-dependent, and peritoneal dialysis effluent was devoid of opsonic activity. These studies suggest that local cellular and humoral mechanisms of defense are inadequate for protection of peritoneal dialysis patients against candidal peritonitis.

Chemiluminescent response to pathogenic organisms: normal human polymorphonuclear leukocytes

Chemiluminescence (CL) is a sensitive indicator of phagocytosis and intracellular killing; however, little is known of the normal CL response by human polymorphonuclear leukocytes to different pathogenic microorganisms. We investigated the luminol-enhanced CL response of normal polymorphonuclear leukocytes to a number of common bacterial pathogens and two yeasts. We analyzed the CL response to viable and heat-killed microorganisms at 25 and 37 degrees C. The CL response to all microorganisms was greater and more rapid at 37 degrees C. Variable responses were observed with viable and heat-killed microorganisms; some were unaffected, whereas other demonstrated reduced CL. Each microorganism caused a reproducible response pattern, which could be placed into two general categories. In the first category were those which caused a rapid exponential rise and decay in CL: Enterobacter cloacae, Salmonella typhimurium, Shigella flexneri, Staphylococcus aureus, Candida albicans, and zymosan. In the second category were those which rose slowly over a longer time course to a poorly defined peak: Pseudomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, and Streptococcus pyogenes. The CL response also reflected serum opsonic activity. The effect of inactivated complement, factor B, and removal of specific antibody were investigated. Increasing the concentration of zymosan gave a proportional rise in peak CL; however, a strain of E. coli caused a variation in peak time rather than peak height. Different CL kinetics were shown for three strains of K. pneumoniae, possibly a result of each having different membrane or cell wall characteristics. This study defines the nature and factors affecting the normal CL response to a variety of common pathogenic microorganisms.