PDL241 binds to plasma cells in rhesus monkey. (A) Immunofluorescence co-staining of PDL241 and anti-CD20 or VS38c in tonsils from normal rhesus monkey. PDL241 staining was green, CD20 and VS38c stained red and nuclei were counter-stained with DAPI (blue). Cells with double staining (PDL241 and VS38c) appeared yellow. (B) IHC staining of PDL241 to draining lymph nodes from normal (N) or collagen immunized (CIA) rhesus monkey. (C). PDL241 but not Fc mutant 241-G2M3 inhibited IgM production from rhesus monkey PBMC stimulated with the TLR-9 agonist ODN2006. CIA, collagen-induced arthritis; DAPI, 4′,6-diamidino-2-phenylindole; IgM, immunoglobulin M; IHC, immunohistochemistry; PBMC, peripheral blood mononuclear cells.