Depression of polymorphonuclear leukocyte functions by purified influenza virus hemagglutinin and sialic acid-binding lectins.

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Abstract
Infection of polymorphonuclear leukocytes (PMNL) with influenza virus causes depression of PMNL metabolic and bactericidal activities. The studies reported here were undertaken to determine whether the hemagglutinin (HA) glycoprotein of influenza virus mediates this depression. PMNL were incubated with purified HA and the oxidative responses to exogenous stimuli were measured. The results indicate that HA, in either liposomes or protein aggregates referred to as rosettes, depressed PMNL oxidative responses. Depression was observed within 2 min of initial interaction of HA with PMNL and lasted more than 2 h. The membrane fusion activity of HA requires proteolytic cleavage of the HA, whereas the receptor binding activity does not. There was no difference in the ability of virions with cleaved or uncleaved HA to depress PMNL responses suggesting that the fusion event is not required for PMNL dysfunction. Inasmuch as the HA glycoprotein binds to sialic acid-containing receptors on the surface of the PMNL, we tested whether other sialic acid-specific binding proteins can mediate the reduction of PMNL responses. Sialic acid-specific lectins from Limulus polyphemus or Limax flavus were incubated with PMNL before measuring their responses to secondary stimulus. Depression was observed upon incubation with the lectins similar to that seen upon incubation with the HA or influenza virus. These results suggest that attachment of influenza virus to sialic acid-containing receptors is responsible at least in part, for suppressing PMNL oxidative responses.