Immunoglobulins on the surface of sheep lymphocytes. II. Class, size and fate during incubation of lymphocytes at 37 degrees C

The BLV-induced leukemia--lymphosarcoma complex in sheep

Sheep are highly susceptible to BLV infection and can be infected via several different means (routes). In all inoculated animals, specific anti-BLV antibodies can be demonstrated 1 to 3 months post-inoculation (p.i.). Between 10 and 13 months p.i., a moderate but persistent lymphocytosis (PL) may be detected in about 50% of the infected animals. This hematological disorder may be, but is not necessarily, associated with the development of a lymphosarcoma and can (might) be interpreted as a true lymphoid leukemia. According to findings revealed by immunolabelling and mitogen stimulation of peripheral blood lymphocytes, BLV-induced PL appears to be a B-cell disorder. Induced lymphosarcoma appears in about 40% of infected sheep during the 6 years p.i. It too is of B-lymphocyte lineage. In vitro studies demonstrate that BLV antigen is expressed exclusively in B-lymphocytes. Yet, BLV expression is greatly stimulated in whole lymphocyte culture by the addition of T-cell mitogen. This same phenomenon occurs when the supernatant of stimulated T-lymphocyte cultures is added to isolated BLV-infected B-lymphocytes. This observation supports the hypothesis that, as is the case with other retroviruses such as HIV, BLV is able to use the regular activation machinery of the immune system for its own replication and transmission. It seems, therefore, that the leukemia-lymphoma complex in sheep may serve as an accurate experimental model for the study of the biological properties of retroviruses.

Calf thymus alkaline phosphatase. II. Interaction with detergents

1. A number of detergents were used to dissolve calf thymus plasma membranes rich in alkaline phosphatase (orthophosporic-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) activity. 2. The Stokes' radius (r) of alkaline phosphatase in each detergent was measured by gel filtraton. The size of the solubilized enzyme varied from r = 6.2 nm in sodium cholate to r = 8.3 nm in Berol EMU-043. With N-alkylsulphates, the apparent size increased with alkyl chain length, with r = 6.4 nm (C9) and r = 7.3 nm (C12). Tween 20 failed to solubilise the enzyme. 3. The effect of each detergent on the catalytic activity of alkaline phosphatase was determined. The non-ionic detergents Triton X-100, Nonidet P-40, Berol EMU-043, Tween 20 and the zwitterionic detergent Empigen BB increased V by 10--50% without substantially altering the Km for p-nitrophenylphosphate. The bile salts sodium deoxycholate and sodium cholate decreased V and increased the apparent affinity of the enzyme for nitrophenylphosphate. Inhibition was concentration-dependent up to the critical micellar concentration, above which it remained constant (deoxycholate, 33% cholate, 76%). Alkylsulphates (C8-12) had no significant inhibitory effect during 24 h at 23 degrees C. 4. Exchanging one detergent for another altered alkaline phosphatase activity to a state characteristic for the second detergent, e.g. the activity of cholate-inhibited alkaline phosphatase was restored to normal levels by excess of Triton X-100 and vice versa. The inhibitory effect of deoxycholate and cholate therefore result primarily from interactions between detergent and alkaline phosphate, rather than from selective removal of lipids from the enzyme. 5. Pure lecithin, lysolecithin and an ether-deoxylysolecithin each reactivated cholate-inhibited alkaline phosphatase in a concentration-dependent fashion. Cholesterol had no effect. 6. The half-life (t1/2) of membrane-bound alkaline phosphatase at 55 degrees C was 64 min. With the exception of Berol, solubilisation in non-ionic detergents caused no marked change in this sensitivity. The enzyme became more labile in deoxycholate (t1/2) = 31 min), but less labile in cholate (t1/2 = 99 min). Alkylsulphates, which are strong denaturants, markedly increased the sensitivity of the enzyme to heat-inactivation (C8, t1/2 = 13 min; C9--12, t1/2 less than 2 min). 7. It is concluded that membrane-bound alkaline phosphatase is separated from most if not all of its neighbouring lipid moieties by these detergents, which bind to the solubilised enzyme. The number and character of molecules binding to the enzyme influence its size and shape, its susceptibility to inactivation and its catalytic activity.

Rapid recovery of antigen-binding receptors on chicken B cells following anti-Ig serum treatment

Rosette-forming cells (RFC) from the peripheral blood of sheep red blood cell (SRBC)-immunized chickens were characterized as B cells which manifest antigen-binding receptors but no antibody secretion. Lymphocytes were pretreated at 0 degrees C with anti-Ig serum, washed, incubated further at various temperatures and harvested for the rosette-forming cells (RFC) assay. Anti-Ig treatment blocked all RFC formation and providing that the cells were maintained at less than 10 degrees C regeneration did not occur up to 6 h. Complete recovery of RFC formation occurred within 10 min at 37 degrees C following treatment with low but not with high concentrations of anti-Ig serum. However, recovery from inhibition by high-dose anti-Ig treatment was achieved by including chicken IgG in the incubation medium. The recovery of receptors was reduced following "sandwich" treatment of lymphocytes. When cells were treated with anti-Ig antibody, washed and exposed to various drug inhibitors of "capping" the regeneration of RFC was prevented; in contrast, inhibitors of protein synthesis were ineffective. The results were interpreted in terms of dissociation of anti-Ig antibodies from the Ig receptor at an early stage of the ligand-induced receptor redistribution process.