Abstract Human SP-D inhibits seasonal, but not pandemic, influenza A virus (IAV). We modified key residues in the carbohydrate recognition domain (CRD) of SP-D to increase antiviral activity. Isolated neck and CRD (NCRD) preparations of SP-D were used. The NCRD of wild type human SP-D did not inhibit IAV (although the full length molecule does). We reported that the substitutions D325A and R343V in the NCRD markedly increase anti-IAV activity in vitro and in vivo. We now report similar activity of a double mutant containing D325S and R343V changes. These double mutants (called D325A+R343V or D325S+R343V) also inhibit pandemic IAV strains. Crystals of D325A+R343V show distinct interactions with viral glycans. D325A+R343V causes marked viral aggregation and increase in IAV uptake by neutrophils and monocytes while wild type SP-D NCRD does not. D325A+R343V inhibits viral protein synthesis in monocytes and suppresses IAV induced tumor necrosis factor (TNF) production. Surprisingly, the wild type human SP-D NCRD also suppresses IAV-induced TNF production without altering viral replication in monocytes. Hence, modification of residues surrounding the lectin site of SP-D markedly increases viral neutralizing and aggregating activity and also broadens the spectrum of inhibited strains. Inhibition of IAV-induced TNF production by monocytes is at least in part mediated by a direct effect on these cells independent of viral neutralization.