Normal antivirus IgM and IgG responses in CD44^−/− mice. Mice were immunized with VSV (2 × 10⁶ pfu IV) and analyzed for neutralizing antibodies in the serum. No differences were seen for neutralizing IgM or IgM between CD44^−/−, ^+/−2, or ^+/+ mice. (closed diamonds, +/+; closed triangles, +/−; open triangles, −/−).