Relationship of Microtubule Organization in Lymphocyte to the Capping of Immunoglobulin

We have used a double fluorescence staining procedure to examine the distribution of antitubulin-staining structures in mouse splenic lymphocytes induced to patch and cap surface immunoglobulin by treatment with antiimmunoglobulin antibodies. A well organized network of fibers, extending from a single microtubule organizing center (MTOC) associated with the centriole pair, was detected by antitubulin staining at all stages of the capping process. In lymphocytes possessing as intact network, the cap was formed and internalized over the region of the cytoplasm containing the organizing center, Golgi apparatus, and most other organelles. In contrast, in lymphocytes which had been subjected to a colchicine treatment sufficient to completely disassemble networks prior to cap induction, no relationship was detected by immunofluorescence between the position of the centrioles (a marker for the MTOC) and the location of the surface cap. Electron microscopic observation of colchicine-treated cells, induced to cap by ferritin-conjugated anti-Ig, revealed extensive disorganization of cytoplasmic organelles and exclusion of organelles from the region of underlying the cap. These results indicate a role for the microtubule network of lymphocytes in maintaining cytoplasmic polarity and in specifying the site of Ig cap formation.