K-antigen-specific, but not O-antigen-specific natural human serum antibodies promote phagocytosis ofKlebsiella pneumoniae

Abstract

Infections due to Klebsiella pneumoniae and other Klebsiella spp. are a leading cause of hospital-associated morbidity, especially in the intensive care setting. In this study, the hypothesis that normal human sera contain sufficient concentrations of K-antigen-specific antibodies to promote phagocytic killing of encapsulated, highly virulent Klebsiella organisms was tested. K2-antigen-specific IgG and IgM antibodies were detected in each of 10 normal sera, and such antibodies were functionally active in a phagocytic killing assay. Phagocytosis depended critically on sufficient numbers of neutrophils and was impaired by the presence of soluble Klebsiella capsular polysaccharide (CPS). Thus, insufficient numbers of neutrophils and circulation of soluble CPS but not lack of K-specific antibodies may be detrimental in Klebsiella sepsis. The efficacy of hyperimmune sera might be based not on enhancement of phagocytosis but on the neutralization of these detrimental effects of circulating CPS and LPS.

Survival of Carbapenem-Resistant Klebsiella pneumoniae Sequence Type 258 in Human Blood

“…2C). Depletion of IgG from NHS significantly increased the survival of NJST258_1 in serum, a finding consistent with the presence of naturally occurring K. pneumoniaespecific antibody (Ab) in NHS (32) and the known ability of antibody to activate the complement cascade (Fig. 2D).…”

“…Shankar-Sinha et al reported similar results with mouse blood during their studies of the role of K. pneumoniae O antigen in bacteremia (47). It is possible that the presence of naturally occurring K. pneumoniae-specific antibodies in normal human serum (32), which are presumably absent in the naive mouse, contributes in part to the noted difference in bactericidal activity. The results of our IgG depletion assays (Fig.…”

Surface antigens contribute differently to the pathophysiological features in serotype K1 and K2 Klebsiella pneumoniae strains isolated from liver abscesses

“…Our study showed that O antigen is a major factor for human serum resistant, but O antigen has been reported not affecting mouse serum resistance [ 18 ]. Besides, normal human sera in one study contained sufficient concentrations of antibodies against K. pneumoniae [ 31 ]. The inconsistency between studies warrants further investigation.…”

Host defence againstC. albicansinfections in IgH transgenic mice with VHderived from a natural anti-keratin antibody

“…However, evidence has shown that specific antibodies make contributions by preventing adherence, toxin neutralization, opsonization, antibody‐dependent cytotoxicity, as well as generating memory antifungal immunity (Magliani et al ., 1997; Han et al ., 1999; Casadevall et al ., 2002; Taborda and Casadevall, 2002; Wozniak et al ., 2002; Montagnoli et al ., 2003; Moragues et al ., 2003). In addition to the specific antibody response, recent studies have revealed that natural antibodies, poly‐reactive antibodies in unimmunized individuals (Boes, 2000; Quintana and Cohen, 2004), may also be important in immunity against microbial infections (Boes et al ., 1998; Ochsenbein et al ., 1999; Shibuya et al ., 2000; Belperron and Bockenstedt, 2001; Lepper et al ., 2003). Thus, B cell‐depleted mice are more susceptible to systemic candidiasis than controls (Maiti et al ., 1985), and B cell knockout mice are easier to develop systemic, but not mucosal, candidiasis (Wagner et al ., 1996).…”