Rosette forming cells

Several indirect arguments have suggested that cyclic AMP (cAMP) may be a second messenger for thymic hormone action. These include the observations that cAMP in the Bach-Dardenne bioassay acts synergistically upon rosette-forming cells with thymulin (Bach and Bach, 1973). In addition, the inductive effects of thymic hormones can readily be mimicked by a variety of products that increase cellular cAMP and conversely can be inhibited by products that decrease cAMP (Scheid et al., 1973, 1975 Astaldi et al., 1978). 

In mice intraperitoneally administered 50 to 450 mg/ kg of the food colorant safflower yellow daily for 8 days, a decrease in serum lysozyme concentration and phago-cytosing functions of both peritoneal macrophages and peripheral leukocytes was observed. The treatment also diminished the production of plaque-forming cells and specific rosette-forming cells, and inhibited the delayed-type hypersensitivity reaction and the activation of T suppressor cells elicited by supraoptimal immunization (Lu et al. 1991). 

The study of the immune response at cellular level was therefore undertaken by two methods the haemolysin plaque forming cells (PFC) assay using the modified Jerne technique" and the rosette forming cells (RFC) test using the method described previously The PFC are the antibody secreting cells (mature or immature plasmocytes) derived from antigen-induced differentiation of B lymphocytes. 

Staining with rhodamine-coupled rabbit anti-POL. a a Rosette-forming cells. 

Edwards, G. E., Miller, R. G., Phillips, R. A. Differentiation of rosette-forming cells from myeloid stem cells. J. Immunol. 105, 719-729 (1970). 

Laskov, R. Rosette forming cells in non-immunized mice. Nature (Lond.) 219,973-975... 

Humoral immunity Plaque forming cell assay Rosette formation, AMP poreforming activity... 

High and Low responders have an equivalent number of natural rosettes formed exclusively by small lymphoc)d es. At the end of the exponential phase, 650 000 RF plasmocytes have differentiated in High line and only 15 400 in Low line. The inter-line difference in the number of RF plasmocytes is 40-fold, which does correspond with the inter-line difference in humoral antibody titre (see Table 5.6). These results indicate that the sharp inter-line difference in antibody synthesis is due to the number of antibody producing cells rather than... 

The rosettes formed by the cell in the intermediate steps of differentiation are about ten-fold more numerous in High than in Low responders. Both the process of plasmocyte maturation itself and the contribution of T derived... 

Chandra, R, K, (1974) Rosette-forming T lymphocytes and cell mediated immunity in malnutrition. Br. Med. J. 3 608. 

The role of sialic acid in the interaction between cells of different origin has been far less studied than in the interaction between identical cells. Cormack (1970) observed a decreased attachment of neuraminidase-treated Walker 25 tumor cells to the mesothelial membrane of rat, but the interpretation of this experiment performed in vivo is complicated by the resynthesis of sialic acid residues at the surface of the treated cell. Weiss and Cudney (1971) found no effect of neuraminidase on the immunolysis of mastocytoma P815 cells by sensitized spleen cells, and it is doubtful that sialic acid residues play a direct role in the interaction between different cells. It may play an indirect one, however, for example, by masking receptor sites at the surface of either human peripheral blood lymphocytes, or sheep red blood cells, as shown by the increased stability of the rosettes formed by these cells upon neuraminidase treatment (Galili and Schlesinger, 1974). 

In the past, evidence has been obtained that cell-mediated immunity in moderate marijuana smokers may be impaired, as judged by the response of their T-lymphocytes to transformation with phytohaemagglutinin (SED VIII, p. 54). Cushman and Khurana (18 ) have since then studied the effects of marijuana smoking on sheep cell rosetting properties of both early (active) and total T-lymphocytes in vitro. Significantly fewer active rosettes were formed by T-ceUs from a population of 35 individuals who appeared to be chronic marijuana smokers than from 34 control subjects. On the other hand, the late (cold-enhanced) rosettes formed by smokers and non-smokers were similar. 

Fig. 7 Freeze-fracture images of hydrogenosomes from T. foetus, a Fractured cell showing a prominent Golgi (G) with several lamellae and fenestrae, as well profiles of endoplasmic reticulum (ER) in close proximity (arrows) with hydrogenosomes (H). Bar = 100 nm. b Hydrogenosomes from an isolated fraction observed by freeze-fracture. Note the clusters of intramembranous particles forming rosettes (arrow). The peripheral vesicle is smooth and does not present clusters of particles or rosettes. Bar = 50 nm. (From Benchimol et al. 2001). c Two freeze-fractured hydrogenosomes exhibiting different fracture planes (arrows). Bar = 100 nm. (From Benchimol et al. 1996a)...

The finished cellulose is in the form of crystalline microfibrils (Fig. 20-29), each consisting of 36 separate cellulose chains lying side by side, all with the same (parallel) orientation of nonreducing and reducing ends. It seems likely that each particle in the rosette synthesizes six separate cellulose chains simultaneously and in parallel with the chains made by the other five particles, so that 36 polymers arrive together on the outer surface of the cell, already aligned and ready to crystallize as a microfibril of the cell wall. When the 36 polymers reach some critical length, their synthesis is terminated by an unknown mechanism crystallization into a microfibril follows. 

Cellulose synthesis takes place in terminal complexes (rosettes) in the plasma membrane. Each cellulose chain begins as a sitosterol dextrin formed inside the cell. It then flips to the outside, where the oligosaccharide portion is transferred to cellulose synthase in the rosette and is then extended. Each rosette produces 36 separate cellulose chains simultaneously and in parallel. The chains crystallize into one of the microfibrils that form the cell wall. 

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