Impairment of phagocytosis by the Klebsiella pneumoniae mannose-inhibitable adhesin-T7 receptor

Abstract

It has been previously shown that Klebsiella pneumoniae K59 carrying the mannose-inhibitable adhesin-T7 receptor (MIAT) efficiently binds to polymorphonuclear leukocytes (PMNs) incubated at 4 degrees C but is not efficiently bound and internalized by phagocytes incubated at 37 degrees C. Pretreatment of K59 with compounds that bind the MIAT ligand (D-mannose, UV-inactivated T7 phages, and pepsin-digested anti-MIAT antibodies) enables PMNs to phagocytize and kill these bacteria. In this article, we show that the incubation temperature has no direct effect on expression of either the MIAT or the PMN receptors. These receptors were always expressed at 37 degrees C when PMNs were treated with substances that impaired their ability to rearrange their surfaces (glutaraldehyde and cytochalasins B and D). Pretreatment of inert PMNs with concanavalin A or succinyl concanavalin A drastically reduced binding of K59 to phagocytes at both 4 and 37 degrees C. The same pretreatment carried out with metabolically active PMNs enabled them to efficiently phagocytize the MIAT-positive strain. When phagocytes were treated with K59 bacteria, they became unable to ingest and kill a K59 mutant not expressing the MIAT which was sensitive to phagocytosis. If this pretreatment was performed in the presence of D-mannose, UV-inactivated T7 phages, and pepsin-digested anti-MIAT antibodies, PMNs maintained their phagocytic activity against the MIAT-negative strain. In the presence of K59 bacteria, a very low chemiluminescence response was generated; in contrast, a significant response was observed when bacteria were previously absorbed with UV-inactivated T7 phages and pepsin-digested anti-MIAT antibodies. These results support our previous suggestion that the MIAT adhesin triggers changes in the cell surface, inhibiting further binding and phagocytosis.