Fig 1.

Degradation of IgM binding to the bacterial surface by viable but not by dead S. suis. (A) Binding of specific IgM antibodies to the surface of S. suis wild-type strain 10 (wt) (27). Wild-type S. suis was incubated with either preimmune or convalescent-phase serum. Immunofluorescence microscopy was conducted with an FITC-tagged polyclonal anti-porcine IgM antibody. (B) Anti-IgM Western blot analysis with a polyclonal antibody (PAB) against porcine IgM of the preimmune and convalescent-phase sera used in experiments shown in panel A. (C, D) Anti-IgM Western blot analysis (PAB) of supernatants of viable and dead S. suis cells incubated for 2.5 h after opsonization with the preimmune (C) and convalescent-phase (D) sera whose blots are shown in panel B. Wild-type S. suis and its unencapsulated mutant strain 10cpsΔEF (Δcps) were killed by either heat inactivation or formaldehyde (FA) treatment. The position of the porcine IgM multimer is marked with an arrow, and the degradation products of porcine IgM are indicated by asterisks. The molecular mass marker is shown on the left of each of the blots.