Complement receptor 3 (CR3) lectin site (CR3 lectin site)

Complement receptor 3 (CR3), also known as Mac-1 or CD11b/CD18, is a heterodimeric integrin receptor primarily expressed on myeloid cells such as neutrophils and macrophages (Vetvicka et al., 1996). The CR3 lectin site is a specific regulatory domain located on the CD11b subunit, distinct from the I-domain, which recognizes and binds to carbohydrate polymers like beta-glucans (Ross et al., 1999). Binding of soluble beta-glucans to this lectin site primes the receptor, enabling it to mediate the killing of iC3b-opsonized tumor cells through a process known as CR3-dependent cellular cytotoxicity (Yan et al., 1999). This site is a key target in cancer immunotherapy, where drugs like Imprime PGG are used to enhance the innate immune system's ability to recognize and destroy cancer cells (Bose et al., 2013). The therapeutic efficacy of targeting this site often depends on the presence of endogenous anti-beta-glucan antibodies to form functional immune complexes (Bose et al., 2013). Beyond oncology, the lectin site plays a role in the recognition of fungal pathogens and the modulation of inflammatory responses (Ross et al., 1999).

Other names

CD11b lectin-like domainMac-1 lectin siteIntegrin alpha-M lectin domainCD11b/CD18 lectin site

Binding of beta-glucan to the lectin site induces a conformational change in the CR3 receptor, priming it to trigger cytotoxic degranulation and phagocytosis upon subsequent binding of iC3b-opsonized targets.