Mixed isotype class II antigen expression. A novel class II molecule is expressed on a murine B cell lymphoma.

Abstract

The structures of Ia molecules expressed by two BALB/c B cell lymphoma lines, A20-1.11 (A20) and 2PK3, were analyzed in an effort to explain the differences in antigen-presenting capacity displayed by these cells. Alloreactive T cell hybridomas specific for I-Ad and antigen-specific, I-Ad-restricted T cells responded well to A20 as the APC. The same alloreactive T cell hybridomas responded weakly or not at all to 2PK3 and the responses of the antigen-specific, I-Ad-restricted T cells were consistently lower to antigen presented by 2PK3 as compared with A20. T cells restricted to I-Ed responded equally well to either A20 or 2PK3 as APC. Additionally 2PK3, but not A20, stimulated a strong syngeneic mixed lymphocyte response. Structural analyses of the Ia antigens revealed that I-A and I-E molecules were expressed by A20, whereas an I-E and a novel I-A-like molecule were expressed by 2PK3. The novel class II molecule was affinity purified from 2PK3 cells using an mAb specific for Ad beta (MK-D6), and this molecule was subsequently shown by an RIA to react with an E alpha-specific mAb (14-4-4S) as well. Chain-specific polyclonal antisera raised against I-A and I-E alpha and beta chains indicated that the 2PK3 "I-A" alpha chain reacted in immunoblot with E alpha-specific and not A alpha-specific antisera, whereas the beta chain reacted with A beta- and not E beta-specific antisera. Peptide map and partial amino acid sequence analyses indicated that the "I-A" molecule expressed by 2PK3 represented a mixed isotype structure resulting from the pairing of Ed alpha with Ad beta. By immunofluorescence staining analysis, 2PK3 did not react with an mAb specific for Ad alpha. 2PK3 was capable of limited antigen presentation through the mixed isotype molecule to I-Ad-restricted OVA-specific T cell hybridomas, although the responses induced were low compared with presentation through I-A on A20. Previous descriptions of the expression of mixed isotype class II molecules in the mouse have resulted primarily from DNA-mediated gene transfer experiments. The results presented indicate that a mixed isotype class II molecule can be expressed naturally.

Lymphoma Immunotherapy with CpG Oligodeoxynucleotides Requires TLR9 Either in the Host or in the Tumor Itself

“…In the special case of B cell malignancies, however, it is possible that the tumor can become its own APC, with increased expression of costimulatory molecules, enabling it to present its own Ags directly to T cells (9,42). A20 cells, an MHC class I-and class II-expressing B cell lymphoma, has long been recognized as a powerful APC (43,44). Indeed, we demonstrated that CpG enhances the expression of CD80 and CD86 on A20 lymphoma cells and it has been shown by others that CpG increases the costimulatory capacities of the A20 lymphoma cells (45,46).…”

In vivo expression and function of hybrid Ia dimers (E alpha A beta) in recombinant and transgenic mice.

“…Since Ea chain cannot be expressed on the membrane by itself, it must be pairing with the surface expression. The existence of an Ea + Aß hybrid molecule has recently been shown in a BALB/c lymphoma (20). We were not able to pick up this hybrid molecule by immunoprecipitation .…”

Rafting MHC-II domains in the APC (presynaptic) plasma membrane and the thresholds for T-cell activation and immunological synapse formation

“…The frequency of stable B-cell/T-cell conjugates (>10 min lifetime) was also much higher with 2PK3 and correlated well with the strength of initial signals. The difference observed in the T-cell stimulating capacity of the two APCs is likely due to two major factors: (i) 2PK3 cells express I-E d and I-E d ␣ /I-A d ␤ mixed isomer forms of MHC-II at the same level as A20 cells express normal I-E d and I-A d forms in comparable extent [36]. This situation results in more potential recognition sites (and maybe higher stability of peptide-MHC complexes) on 2PK3 than on A20 cells for IP12-7 T-cells.…”