Mechanisms of Lymphocyte Transformation

The application of lectins to the characterization and isolation of mammalian cell populations

Mammalian cells invariably contain a vast array of glycosylated moieties, both inside the cell and on the cell surface. There is an increasing awareness of the utility of these carbohydrates in delineating the phenotype or function of many populations of cells. To this end lectins are extremely useful reagents. Lectins are carbohydrate-binding proteins and glycoproteins of non-immune origin derived from numerous plants and animals. A wide variety of lectins with many distinct carbohydrate specificities have been isolated. Historically the most common laboratory techniques utilizing lectins have been agglutination, mitogen stimulation, and fluorescence techniques. Recent advances in the development and conjugation procedure for labels and matrices have led to the creation of numerous novel lectin-based assays. Lectins are currently used not only to identify cells with specified carbohydrate groups, but also to quantitate the carbohydrate groups or to isolate the carbohydrate-bearing cells or structures.

Transfer ribonucleic acid populations in concanavalin-A-stimulated bovine lymphocytes

Transfer RNA isolated from lymphocytes stimulated by concanavalin A and that from resting cells were compared with respect to amino-acid acceptance, integrity of the CCA-terminus, extent of modification and isoacceptor distribution. Following growth stimulation the overall amino-acid acceptance of the tRNA is elevated, in particular the relative acceptor activities for threonine and arginine are increased. The reduced acceptor activity of the tRNA from the quiescent cells is not due to a preferential degradation of the CCA-end, since it persists even in the presence of ATP(CTP):tRNA nucleotidyltransferase. We therefore conclude that this reduced activity is caused by structural differences of the tRNAs. The content of modified nucleotides in newly synthesized tRNA from lymphocytes cultured in the presence and absence of concanavalin A was determined. tRNA from resting cells was found to be undermodified with respect to pseudouridine and dihydrouridine. Upon monitoring the tRNA isoacceptor distribution by affinity chromatography on immobilized elongation factor Tu and subsequent two-dimensional gel electrophoresis, a preferential synthesis of particular lysine- and threonine-accepting tRNAs was observed upon mitogenic stimulation. Evidently, a specific tRNA population is needed by the proliferating cells. These results are discussed in view of the hypothesis that the commitment of lymphocytes to proliferation is at least in part under translational control.

Mitogen effects on lipid metabolism during lymphocyte activation

Mitogenic and non-mitogenic lectins have been compared for their abilities to stimulate acetate and choline incorporation into mouse spleen lymphocyte lipids. The concns required for maximal acetate incorporation correspond to those required for maximal blastogenesis. The non-mitogenic lectins tested had no effect on acetate incorporation. Concanavalin A also stimulated acetate incorporation into splenic lymphocyte lipids of athymic mice which do not undergo T-cell blastogenesis. 4,4'-Diaminodiphenylsulfone (dapsone) at 150 micrograms/ml inhibited the incorporation of choline into mouse spleen lymphocyte phosphatidylcholine by 40%, but had no significant effect on concanavalin A induced mitogenesis when the inhibitor was present during the first few hours of transformation. Enhanced turnover of phospholipids appears to be a parallel but non-essential event in the early stages of mitogenesis.

Hematologic and immunologic effects of pulsed microwaves in mice

Mice were exposed in the far field in an anechoic chamber to 2,880-MHz pulsed microwaves 3 to 7.5 h daily, 5 days/week for 60 to 360 h. Three experiments were performed at average power densities of 5 mW/cm2 and six at 10 mW/cm2, corresponding to averaged specific absorption rates (SARs) of 2.25 and 4.50 mW/g, respectively. Each experiment consisted of eight mice, with a concurrently sham-exposed group of eight. In two of three studies at 5 mW/cm2, there was a significant increase in bone marrow cellularity in the microwave-exposed groups compared to the sham-exposed groups. Significant differences were occasionally seen in erythrocyte, leukocyte, and platelet values from microwave-exposed groups, but were not consistently observed. In one of six groups exposed at 10 mW/cm2, mean bone marrow cellularity was reduced significantly in the microwave-exposed mice; in another group, the lymphocyte count was increased. In only one exposure (10 mW/cm2 for 360 h) was any significant effect noted on serum proteins: a reduction to 5.1 +/- 0.3 g/dl in the exposed versus 5.6 +/- 0.4 g/dl in the sham-exposed mice. This was due to a decrease in alpha and beta globulins, with no effect on albumin or gamma globulin concentrations. No effect on bone marrow granulocyte/macrophage colony-forming units (CFU) was revealed following exposure of mice to pulsed microwaves at 5 mW/cm2. In one of four exposures at 10 mW/cm2, there was a significant increase in CFU-agar colonies. No significant effects of exposures at 10 mW/cm2 were observed on in vivo and in vitro assays of cell-mediated immune functions. No exposure-related histopathologic lesions were found from examination of several tissues and organs. Results of these series of exposures of mice at SARs of 2.25 and 4.50 mW/g indicated no consistent effects on the hematologic, immunologic, or histopathologic variables examined.

Effects of 60 Hz-electric fields on specific humoral and cellular components of the immune system

We evaluated humoral and cellular functions of the immune system of Swiss-Webster mice exposed to 60-Hz electric fields at 100 kV/m. No significant differences were observed in primary antibody response to keyhole limpet hemocyanin (precipitating antibody levels) between exposed (30 to 60 days) and control mice, nor were there significant changes in mitogen-stimulation response of spleen cells from mice similarly exposed for 90 or 150 days when compared to sham-exposed animals.

The role of serine hydroxymethyltransferase in cell proliferation: DNA synthesis from serine following mitogenic stimulation of lymphocytes

It is shown that the time-course of incorporation of radioactivity from [3-14C]serine into nucleic acids parallels DNA synthesis following mitogenic stimulation of human peripheral blood lymphocytes by phytohaemagglutinin (PHA). The activity of serine hydroxymethyltransferase was elevated about four-fold in PHA-stimulated lymphocytes compared to that in unstimulated control cells. It is suggested that lymphocytes, in common with other proliferating cell systems, may synthesize serine de novo for utilization in pathways of nucleotide biosynthesis following mitogenic stimulation.