BOTH INVARIANT CHAIN ISOFORMS II31 AND II41 PROMOTE CLASS-II ANTIGEN PRESENTATION

The invariant chain (li) gene encodes two differentially spliced varia nts li31 and li41. The li31 isotype is the dominant form expressed in all antigen-presenting cells (APC). li41 is differentially expressed a nd can be found in large quantities in Langerhans and dendritic cells. While a functional role of ii in class II antigen presentation is now well established, a distinct role of the ii isotypes remains controve rsial, We tested li31 and li41 L cell transfectants for antigen presen tation of hen egg lysozyme (HEL) to T cell hybridomas, The result indi cates that both ii chains promote antigen presentation equally well. T o test other APC than transfected L cells, we introduced a recombinant li41 gene into an li-deficient mouse line. There the transgene induce s about one-third of total ii expression of wild-type mice. Surface ex pression of class ii molecules and the CD4 compartment which are defic ient in li knock-out mice are restored in li41 transgenic mice. B lymp hocytes from li41 transgenic mice and li31-expressing B lymphocytes fr om wild-type mice were used as APC for presentation of keyhole limpet hemacyanin and ovalbumin to T cell hybridomas. The results show that b oth li chains facilitate antigen presentation equally well.