Presentation of nontargeted OVA is enhanced by BCR and FcαR/WT γ-chain cross-linking but not by cross-linking of FcαR with altered γ chain.

IIA1.6 cells expressing FcαR and either (A) WT γ chain, (B) γ chain with IIA ITAM, or (C) γ chain with Y → F mutation were incubated with increasing concentrations of OVA with (indicated by cross-hatched bars) or without (indicated by black bars) 10 μg/mL antimouse IgG in the presence of DO-11-10 T cells. Transfectants with FcαR and either (D) WT γ chain, (E) γ chain with IIA ITAM, or (F) γ chain with Y → F mutation were also incubated with OVA with (indicated by cross-hatched bars) or without (indicated by black bars) 1:5 diluted My43 anti-FcαR IgM hybridoma supernatant and 10 μg/mL anti– mIgM in the presence of DO-11-10 T cells. Supernatants were harvested and assayed for IL-2, a measure of antigen presentation, as described in “Materials and methods.” Numbers above histogram bars denote IL-2 titers. A difference in titer of 4-fold or more is significant. Similar results were obtained in 3 separate experiments.