Biosynthesis of immunoglobulin A (IgA). Secretion and addition of carbohydrate to monomer and polymer forms of a mouse myeloma protein

Cell suspensions of mouse plasma-cell tumour MOPC 315 secreting predominantly IgA (immunoglobulin A) monomer and dimer were incubated with radioactive leucine, mannose, galactose and fucose for various periods of time. The amounts of secreted and intracellular immunoglobulins were measured by co-precipitation with specific antibody, and the molecular species present were assessed by electrophoresis in polyacrylamide gels. Analysis of the secreted myeloma protein demonstrated that monomer and dimer IgA molecules are identical with respect to carbohydrate composition and rate of secretion. Within the cell, the myeloma protein is almost entirely accounted for by monomer units which either leave the cell as such or are polymerized with the addition of J chain close to the time of secretion. The results support the concept of a stepwise addition of carbohydrate residues to IgA immunoglobulin during the process of secretion. Similar patterns of carbohydrate assembly were found for the monomer or dimer molecules. Mannose residues are added at an early stage, whereas fucose is added close to the time of secretion. Galactose is also added early, but some may also be incorporated at a later stage. Control of IgA polymerization is considered unlikely to reflect regulation at the level of carbohydrate addition, and it is suggested that the critical controlling factor is the J chain.     

Hierarchy of cytotoxic T cell clones. II. Intraclonal triggering of lysis by hapten-specific CTL

Cells from clones of anti-hapten murine cytotoxic T lymphocytes (CTL) can act as both target and effector cells, but will not lyse members of the same clone. The effect of haptenation on the cytolytic activity of anti-fluorescein (FL) and anti-trinitrophenol (TNP) CTL clones was examined. Treatment of anti-FL clones with fluorescein isothiocyanate or anti-TNP clones with trinitrobenzene sulphonic acid induces these clones to kill in an antigen-independent fashion. Targets killed by the haptenated CTL included syngeneic and allogeneic B lymphocyte blast cells, P815, YAC-1 and in one case human GM 4072 tumor cells. The importance of CD8 and T cell receptor (TCR) occupancy is demonstrated by the ability to block autotriggering by antibody directed against Ly 2 and the TCR. The results demonstrate that effects other than antigen recognition of the target play a role in the final outcome of effector-target cell interactions and provide a mechanism which could lead to autodestruction and immunosuppression particularly in some types of viral infection.     

Function of the delipidated beta-adrenergic receptor appears to require a fatty acid or a neutral lipid in addition to phospholipids

Detergent-solubilized preparations of the beta-adrenergic receptor (R) and of the guanyl nucleotide binding proteins (Gs) were extensively treated to remove phospholipids and cholesterol. Reconstitution of an R-Gs system was subsequently performed in the presence of a mixture of natural phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine or the synthetic dioleoyl derivatives of the same phospholipids. In both cases, an additional lipid was required for the agonist-dependent activation of Gs. The requirement could be fulfilled by alpha-tocopherol, or by unsaturated fatty acids such as oleic acid. Inclusion of this non-phosphorylated lipid in the reconstituted system enhanced the isoproterenol-dependent activation of Gs by guanosine 5'-O-[gamma-thio]triphosphate 16-33-fold. The rate of activation was largely dependent on the addition of the agonist. Efficient functional reconstitution of R-Gs was thus achieved in a totally defined lipid system. Additional studies of the reconstituted system and of the native membrane led to the notion that the non-phosphorylated lipid plays a role in the function of the hormone-R complex.