Multimerization of Surfactant Protein D, but Not Its Collagen Domain, Is Required for Antiviral and Opsonic Activities Related to Influenza Virus

Abstract

Surfactant protein D (SP-D) plays important roles in the initial innate defense against influenza A virus (IAV). The collagen domain of SP-D is probably critical for its homeostatic functions in vivo and has been implicated in the modulation of macrophage responses to SP-D-ligand complexes. For the current studies, we used a panel of rat SP-D mutants lacking all or part of the collagen domain to more specifically evaluate the contributions of this domain to viral interactions. SP-D multimers lacking the collagenous sequence efficiently neutralized Phil82 IAV, promoted neutrophil uptake of IAV, and also potentiated the IAV-induced neutrophil respiratory burst response. A dodecameric mutant with shortened collagenous arms showed enhanced viral aggregation and neuraminidase inhibition, and an increased capacity to inhibit a partially collectin-resistant strain of IAV. By contrast, truncated molecules lacking an N-terminal and collagen domain showed no detectable antiviral and opsonizing activity, despite preservation of lectin activity and detectable viral binding. Thus, multimerization, which is mediated by the N-peptide, is more important than the collagen domain for efficient viral neutralization and opsonization. However, the structure of the collagen domain significantly influences the anti-viral activity of multimerized forms of SP-D.

A Unique Sugar-binding Site Mediates the Distinct Anti-influenza Activity of Pig Surfactant Protein D

“…For all strains, however, it was clearly demonstrated that RpNCRD exhibits HA inhibitory activity, in contrast to RhNCRD for which no activity could be measured in this assay. Dodecameric oligomerization thus appeared to be essential for native hSP-D to express its HA inhibitory activity, as determined previously (57,58), driven primarily by the aggregation properties of the fully assembled hSP-D molecule.…”

Viral aggregating and opsonizing activity in collectin trimers

“…Our results convincingly show, however, that trimeric collectin hSP-D-NCRDs can also act as opsonins to enhance neutrophil or monocyte/macrophage uptake of IAV. We have recently shown that small dodecamers of SP-D lacking the collagen domain but retaining the NH 2 terminus and hSP-D-NCRD trimers cross-linked with MAbs also promote neutrophil uptake of IAV (32,34). Hence, using several methods, we have shown that the collagen domain per se in not required for antiviral or opsonizing activity.…”

Mutagenesis of Surfactant Protein D Informed by Evolution and X-ray Crystallography Enhances Defenses against Influenza A Virus in Vivo

“…The capacity of SP-D to aggregate IAV is dependent on higher order multimeric structure, and trimeric NCRDs are devoid of aggregating activity (35). However, we recently observed that trimeric NCRDs with the R343V substitution can efficiently aggregate Phil82 but not SP-D resistant strains (27,36).…”