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Anti-Immunoglobulin Stimulation of Murine Lymphocytes

II. Identification of Cell Surface Target Molecules and Requirements for Cross-Linkage¹

From the Division of Clinical Immunology, Departments of Medicine and Microbiology, University of Colorado Medical School, Denver, Colorado 80220, and Department of Allergy and Clinical Immunology, National Jewish Hospital and Research Center, Denver, Colorado 80206

Abstract

Splenic B cells from normal mice, 7 months of age or older, can be stimulated to proliferate in vitro with soluble anti-immunoglobulin (Ig) reagents. To investigate whether the integrity of the anti-Ig molecule is necessary for stimulation and to determine whether cross-linkage of cell surface Ig is required, experiments were done by using F (ab')₂ fragments and Fab monomers prepared from anti-MIgM serum. To determine whether antibodies directed against heavy chains would induce cell proliferation, class-specific antisera were prepared and tested. The results showed that cell proliferation was induced by F (ab')₂ fragments but not by Fab monomers. In addition, cell proliferation was obtained with monospecific antiserum directed against µ heavy chains but not with antisera directed against - or - chains. Thus cross-linkage of µ heavy chains on the B cell surface is required for soluble anti-Ig-induced proliferation. Further experiments were done to investigate the nature of the age-associated response by comparing membrane immunoglobulin density and class on spleen cells from old and young (2 to 3 months) mice; no differences in surface immunoglobulins were found which would explain the age-associated response to anti-Ig reagents.

Footnotes

¹ Supported in part by National Institutes of Health Grants AG00464 and AI-12136, American Heart Association Grant 74-856, and the Colorado Multiple Sclerosis Society.

² Fellow of the Colorado Multiple Sclerosis Society. Present address: Department of Microbiology, Harvard Medical School, 25 Shattuck Street, Boston, Massachusetts 02115.