T cell-independent B cell response to self-monosialogangliosides: primary response monoclonal antibodies.

Purified GM1 and GM2 gangliosides incorporated into liposomes were injected subcutaneously in BALB/c mice every 3-4 days after pretreatment of the animals with low-dose cyclophosphamide. Serum samples were collected at different intervals and tests by ELISA for the presence of anti-ganglioside antibodies. Four doses (50 micrograms each) were sufficient to raise a measurable primary type of response to GM1, while nine doses were required to obtain measurable IgM antibody titers to GM2. Three monoclonal antibodies (MAbs) wer generated by fusing splenocytes with mouse myeloma cells. The specificity of MAbs was determined by ELISA and HPTLC-immunostaining using a panel of purified glycolipids. The MAb designated E1 showed a high degree of specificity because it reacted only with N-acetyl GM2. Monoclonal antibody A3 reacted predominantly with GM2 and GM1, but also reacted moderately with the GM3 ganglioside. The epitope recognized by this MAb is suggested to be the trisaccharide sequence GalNAc beta 1-4(NeuAc alpha 2-3)Gal. The third MAb (F6) reacted strongly with GM1 but a weak reactivity was also observed with GD1b as well as with asialo-GM1, indicating that the terminal tetrasaccharide Gal beta 1-3GalNAc beta 1-4(NeuAc alpha 2-3)Gal- structure is probably involved in antigenic recognition. Formalin-fixed and paraffin-embedded tissue sections were stained with the E1 and A3 MAbs, using the avidin-biotin complex (ABC) technique. Strong immunoreactivity for E1 appeared in the tumor cells of five primary lung carcinomas and in five malignant melanomas. No immunoreactivity was demonstrated in the parenchyma of a lung without malignancy, or in a metastasis from a colon carcinoma.

Antigen-specific primary immune response of human B-lymphocytes after in vitro immunization with GM3 ganglioside.

In vitro immunization of human B-lymphocytes was performed with liposomes containing the monosialoganglioside GM3, with or without either complete tetanus toxoid or a synthetic T helper epitope derived from tetanus toxin (determinant 830-843). The immunized B-cells were Epstein-Barr virus transformed and the human anti-ganglioside antibody response was evaluated using an indirect ELISA against different mono- and disialogangliosides. Clones producing antigen-specific human antibodies of the IgM isotype against the ganglioside GM3 used as the immunogen were selected and one clone, IM-11, was further characterized. In addition, a method of positive selection using GM3-coated magnetic beads has been developed which allowed us to rescue unstable clones. The binding of the human antibody IM-11 to a large panel of glycosphingolipids separated on thin-layer plates was studied. The human MAb IM-11 was found to bind strongly to NeuAcGM3, IV3 NeuAcnLc4 and sulfate containing glycosphingolipids and weakly to NeuGcGM3. Immunohistological staining of melanoma and breast cancer biopsy sections showed a selective reactivity of IM-11 with tumor cells which varied among different tumors.