The sensitivity of antibody to 2‐mercaptoethanol treatment in three Australian marsupials

Abstract

Antibody in Australian marsupials 359Saturation of most of the relevant AMS receptors occurred at a serum concentration of about 1.5 % as suggested b y the biphasic curve obtained by AMS titration (Fig. 3). This concentration could be quantitively related t o the number of cells in the culture (unpublished data). The steep slope observed a t low AMS concentrations was probably due to the binding of antibodies to the free macrophage receptors. At a serum concentration of about 1.5 %, receptor saturation seemed complete. The moderate slope at higher concentrations was probably due t o different equilibrium states between AMS receptors and the antibodies in excess. A similar titration of antiserum might b e a useful method for the estimation of the relative amounts of antibody receptors present on the cell surface.The shedding and subsequent reappearance of the relevant antigens on the cell surface suggests that a dynamic state exists in macrophage membranes. The physiological significance of the phenomenon of blocking antibody activity by cells against which they are directed is subject t o speculation. Possibly, the escape of either malignant or normal cells from antibody-mediated cytotoxic effect is due t o a similar blocking that takes place in vivo.The shedding of antigens from cultured cells into their growth media occurs most likely in other cell systems. Separation of these components from the culture media may be a valuable method t o isolate and characterize membranal antigens. We wish to express our gratitude to Prof: P. Minden for his critical review of the manuscript. l%is study was supported by research grants from Concern Foundation, Mr. and Mrs. F. Lautenberg and Mr. and Mrs. L. Tisch.Immunological responses t o injections of sheep erythrocytes, Salmonella adelaide flagella and bacteriophage @X 174 were investigated in three species of Western Australian marsupials (Setonix brachyurus, Macropus eugenii and Trichosurus uulpecula).Two classes of immunoglobulins similar t o the eutherian IgM and IgG were normally formed t o the antigens. In addition, a low molecular weight anti-phage a x 1 7 4 antibody of about 80 000 daltons was present in the three species. In Setonix the 19 S antibody converted t o 7 S type relatively slowly in the primary response, but rapidly in the secondary response. The 2-mercaptoethanol treatment showed that both 19 S and 7 S antibody was sensitive in variable proportions ranging from 0 t o 100 % and a different lability was noted t o each of the antigens in the three species.In general, results indicated that the immune response in the marsupials did not lack the important features which typify an immune response in eutherians.

Biological Considerations of the Marsupial-Placental Dichotomy

“…I am in no way suggesting that "placentals" have been derived from "marsupials," but rather only emphasize the close phylogenetic relationship of the two groups and the likely existence of morphologically and physiologically highly advanced viviparous therian mammals in the Early Cretaceous. As examples, it seems unlikely to me that the great similarities between marsupials and placentals in the immune system (Block, 1964;Yadav, 1973), in the basic mechanisms of temperature control (Dawson, 1973), and even in brain rhythms during sleep (Tauber, 1974, p. 164) would have been complete parallelisms not present in the common ancestor; there are simply too many such profound similarities. In contrast to the beliefs of some authors (see, for example, Tyndale-Biscoe, 1973, p. 189), I feel that we can learn a great deal about mammalian adaptations to the Early Cretaceous environment through the cautious study of living kinds.…”