The β-Glucan-Binding Lectin Site of Mouse CR3 (CD11b/CD18) and Its Function in Generating a Primed State of the Receptor That Mediates Cytotoxic Activation in Response to iC3b-Opsonized Target Cells

Abstract

Mouse leukocyte CR3 (Mac-1, αMβ2 integrin) was shown to function as a receptor for β-glucans in the same way as human CR3. Soluble zymosan polysaccharide (SZP) or pure β-glucans labeled with FITC or 125I bound in a saturable and reversible manner to neutrophils, macrophages, and NK cells. This lectin activity was blocked by anti-CD11b mAb M1/70 or 5C6 and did not occur with leukocytes from CR3−/− (CD11b-deficient) mice. SZP preparations containing primarily mannose or glucose bound to CR3, and the binding of 125I-labeled β-glucan to CR3 was competitively inhibited by β-glucans from barley or seaweed, but not by yeast α-mannan. Also, as with human CR3, the lectin site of mouse CR3 was inhibited by α- or β-methylglucoside (but not d-glucose), α- or β-methylmannoside, and N-acetyl-d-glucosamine. Phagocytosis of zymosan and serum-opsonized zymosan was partially inhibited by anti-CR3 and was reduced to <40% of normal with leukocytes from CR3−/− mice. As with neutrophils from patients with CD18 deficiency, neutrophils from CR3−/− mice exhibited no phagocytosis of particulate β-glucan. SZP or β-glucans primed CR3 of neutrophils, macrophages, and NK cells for cytotoxicity of iC3b-opsonized tumor cells that otherwise did not trigger killing. β-Glucan priming for cytotoxicity was inhibited by anti-CR3 and did not occur with leukocytes from CR3−/− mice. The primed state of macrophage and NK cell CR3 remained detectable for 18 to 24 h after pulsing with β-glucans. The similarity of mouse and human CR3 in response to β-glucans highlights the utility of mouse tumor models for development of therapeutic β-glucans.

Sialylation regulates neutrophil transepithelial migration, CD11b/CD18 activation, and intestinal mucosal inflammatory function

“…In addition to CD11b/CD18 glycosylation effecting functional outcomes, previous work has demonstrated that CD11b binding to fucosylated glycans regulates PMN epithelial adhesive interactions in the intestine ( 52 , 67 ). Interestingly these data highlight that PMN CD11b/CD18 can act both as a ligand for carbohydrate binding proteins and as a lectin-like mediator that can itself engage glycans to effect regulation of cellular functions ( 68 , 69 ). Interestingly, in contrast to inhibitory effects observed for degranulation and superoxide release, increased levels of PMN phagocytosis were observed downstream of sialidase inhibition.…”

A LTB4/CD11b self-amplifying loop drives pyogranuloma formation in chronic granulomatous disease

“…This corroborates the findings of Song et al., 16 where the CGD neutrophil production of LTB 4 was dependent on cell density. While a search for CD11b ligands proved unproductive, β-glucan, a major component of zymosan particles, has also been shown to bind to CD11b 52 and is still a possibility. Although we did not find a requirement for zymosan particles as a nidus for forming aggregates in live cell time-lapse imaging experiments, it is possible that β-glucan freed from zymosan particles is bound by CD11b and propagates inflammatory signaling.…”

OMIP‐100: A flow cytometry panel to investigate human neutrophil subsets

“…Upon activation, neutrophils undergo priming for transmigration into the injured or infected tissue. Classical rolling/adhesion markers of neutrophil migration CD11b (also known as MAC-1) and CD62L (also known as L-selectin) are included in the panel to assess the migratory state [43,44]. In addition, primary and secondary granule exocytosis following migration can be determined by measuring the surface expression of CD63 and CD66b, respectively [45][46][47][48].…”