THYMUS-DERIVED (T) CELL IMMUNOGLOBULINS : PRESENCE OF A RECEPTOR SITE FOR IGG AND ABSENCE OF LARGE AMOUNTS OF "BURIED" IG DETERMINANTS ON T CELLS

Quantitation of surface and total cell Ig obtained after lysis by detergent, urea-acid treatment, and freeze-thawing were determined on spleen cells, thymus cells, and spleen cells specifically depleted of B cells. A two- to four-fold increase in measurable Ig was found after cell lysis. All cell populations showed a similar increase in measurable Ig indicating that no discordantly large amounts of buried Ig determinants were associated with the surface of T cells. The lack of appreciable amounts of T cell Ig was confirmed by immunoprecipitation of radioiodinated cells. A theta-positive lymphoma was described which, when grown in culture, lacked detectable surface Ig but contained a receptor site for IgG. This resulted in appreciable amounts of surface IgG being associated with the tumor line when isolated from ascitic fluid of tumor-bearing mice or after preincubation of cultured cells with either heat-aggregated IgG or normal mouse serum

IMMUNOGLOBULINS ON THE SURFACE OF LYMPHOCYTES : I. DISTRIBUTION AND QUANTITATION

The distribution, and quantity of immunoglobulins on the surface of lymphocytes has been studied by means of immunofluorescence and a quantitative radio-immunoassay. Surface immunoglobulins were found on approximately 45% of spleen and marrow lymphocytes and 7–14% of lymphocytes from lymph nodes, peripheral blood, and peritoneal exudate. Thymic lymphocytes contained undetectable amounts of immunoglobulin. In the spleen the different immunoglobulins were present in the following order: γG2 > γG1 > M > γA > γG3. The surface immunoglobulin was largely removable by brief treatment with trypsin. Quantitative analysis indicated that 50,000–150,000 molecules of immunoglobulin were present on an individual cell. A variety of observations make it likely that this lymphocyte-associated immunoglobulin. is a product of the cell to which it is attached rather than a form of cytophilic antibody

Hydrodynamic induced deformation and orientation of a microscopic elastic filament

We describe simulations of a microscopic elastic filament immersed in a fluid and subject to a uniform external force. Our method accounts for the hydrodynamic coupling between the flow generated by the filament and the friction force it experiences. While models that neglect this coupling predict a drift in a straight configuration, our findings are very different. Notably, a force with a component perpendicular to the filament axis induces bending and perpendicular alignment. Moreover, with increasing force we observe four shape regimes, ranging from slight distortion to a state of tumbling motion that lacks a steady state. We also identify the appearance of marginally stable structures. Both the instability of these shapes and the observed alignment can be explained by the combined action of induced bending and non-local hydrodynamic interactions. Most of these effects should be experimentally relevant for stiff micro-filaments, such as microtubules.Comment: three figures. To appear in Phys Rev Let