A broad range of
plant lectins have recently been shown to inhibit the infectivity of herpes simplex virus type 1 (HSV-1) in vitro. We decided to investigate the role of mammalian
lectins in
infection with herpes simplex virus. Two
lectins,
conglutinin and
mannan-binding protein (also called
mannose-binding protein, MBP), belonging to the
collectin family of
lectins, were examined. Four week-old BALB/c mice were injected subcutaneously with 100 micrograms bovine
conglutinin or 50 micrograms human MBP 1 day before intravenous
infection with 5 x 10(4) PFU of herpes simplex virus type 2 (HSV-2). A three-fold increase in virus titre of the liver was observed on day 3 of the
infection in the mice pretreated with
conglutinin or MBP, whereas no effect was seen on days 1 and 5. In a standard plaque assay using Vero cells we were not able to demonstrate reproducibly either
infection inhibition or
infection enhancement, when virus was pre-incubated with differing concentrations of the
collectins. The concentrations used were similar to those used by us in vivo, and by others in in vitro experiments showing inhibition of the infectivity of HSV-1 with
plant lectins. In an ELISA with HSV-2
antigens captured on anti-HSV-2
antibodies,
calcium-dependent and
carbohydrate inhibitable binding of the
collectins was observed. Our results indicate that the effect of endogenous mammalian
collectins in vivo may not be neutralization as suggested by the data using
plant lectins. Instead, the previously described opsonizing activity of the mammalian
collectins may provide the virions with an alternative port of entry into cells leading to
infection enhancement.