Search PubMed⌕ Search

Biomedical subjects

S K Singhal

Publications and source records attributed to S K Singhal.

At least 55 records · Page 3Linked to original sources
PubMed1981

Immunogenicity and characterization of supernatant DNA released by murine spleen cells.

The cellfree supernatant from cultured splenocytes contains an immunogenic molecule capable of inducing anti-DNA antibodies in vitro and in vivo in young preautoimmune NZB/W and some normal mouse strains. The response to this supernatant material does not reflect polyclonal activation, and the molecule responsible for its immunogenic activity appears to be a relatively small (approximately 150 base pairs) DNA molecule, predominantly (75 to 80%) double stranded with tail-end single-strand regions. It does not appear to contain any unusual secondary structure. This immunogenic DNA molecule can be recovered from cultures of some normal as well as young B/W mice. It contains no observable protein moiety, and after phenol-chloroform extraction, the immunogenic DNA migrates on polyacrylamide and agarose gels as a relatively narrow homogeneous band. The anti-DNA antibody response detected in the serum of mice after injection of this DNA molecule appears to have its greatest affinity for the homologous DNA and for undenatured calf thymus DNA. Unique base sequences do not appear to be responsible for its immunogenic effects. Rather, this may depend on its relatively small size, since calf thymus DNA sheared to a similar size and also found incapable of digestion with restriction endonucleases had a similar immunogenic effect.

Animals↗
PubMed1980

Induction of anti-ssDNA antibodies in normal and preautoimmune mice in vivo.

Splenic lymphoid cells of normal and preautoimmune mice escape normal regulatory mechanisms in vitro and spontaneously synthesize anti-ssDNA antibody in the absence of any exogenous antigen. In addition, both the cultured cells and their cell-free supernatants were capable of inducing specific anti-ssDNA responses in vivo upon their injection into syngeneic recipients. The response was host-derived, required the participation of B and T cells, and was not due to polyclonal activation. The immunogen responsible for this response appeared to be membrane-associated, was found predominantly on cultured T cells, and was sensitive to DNase and proteolysis.

Animals↗
PubMed1979

A tumor T cell line which can be specifically activated by antigen.

We have shown that permanently transformed T cells of a leukemic line (485-2) maintain their immunocompetent function and can be specifically activated by antigen. This cell line should facilitate investigations into the biochemical mechanisms of T cell activation and may help elucidate the nature of the T cell receptor.

Animals↗
PubMed1979

Immunological senescence. II. Normal in vitro colony formation by B cells from old mice.

The in vitro frequency and proliferative capacity of B cells and B-cell precursors in old mice was assessed. The mitogenic response to the B-cell mitogens lipopolysaccharide (LPS) and dextran sulphate decline later and at a slower rate than the T-cell response to phytohaemagglutinin and concanavalin A. The response to precursor B-cell mitogen dextran sulphate was not depressed in the bone marrow of aging mice. In addition, the dose response and kinetics of LPS and mercaptoethanol stimulated B-cell colony formation in agar was identical in spleen cells from young and old mice. These results indicate that the intrinsic proliferative capacity of B cells from old mice is normal.

Aging↗
PubMed1978

Loss of self-tolerance to single-stranded deoxyribonucleic acid (sDNA) in vitro.

The spleens of many normal and autoimmune-susceptible strains of mice mount a specific, IgM, anti-sDNA plaque-forming cell (PFC) response in vitro in the absence of an exogenous source of antigen. This response was not related solely to levels of xenotropic or ecotropic virus and was generated from a small number of precursor cells capable of binding sDNA. Small numbers of anti-sDNA PFC were also apparent in serum-free medium and the response of low-responder strains could be augmented with pokeweed mitogen. T cells and macrophages were not essential and cell division was required early in culture to obtain a peak response on day 5. These results suggest that autoantigen-sensitive cells may escape normal regulatory mechanisms in vitro and differentiate into clones of autoantibody secreting cells.

Animals↗
PubMed1978

Regulation of the autoimmune plaque-forming cell response to single-strand DNA (sDNA) in vitro.

We have shown that young autoimmune and normal strain mice possess autoantigen-sensitive cells potentially capable of producing anti-sDNA autoantibody in the absence of normal regulatory mechanisms in vitro. In certain strains such as B/W mice, these regulatory mechanisms presumably break down with increasing age, and autoimmunity develops. These regulatory mechanisms might consist of sDNA, T cells, or some combination of these since both of these agents suppressed the anti-sDNA PFC response in vitro. The sDNA may have inhibited PFC development by a receptor blockade mechanism since i) spleen cells pulsed with sDNA for short periods and then washed were suppressed after 5 days of culture; ii) treatment of these blocked cells with trypsin and DNase I restored the anti-sDNA response; iii) the PFC remaining in partially blocked cultures were of lower avidity than PFC in unblocked cultures; and iv) the target of sDNA may be a B cell. Thymocytes and splenic T cells suppressed the anti-sDNA response but not the anti-SRBC response in vitro in a dose-dependent manner. The suppressive capacity of thymus cells did not decline with age in B/W mice. In addition, thymus cells activated by competing foreign antigens could also suppress the anti-sDNA response. The relationship between these modes of regulating autoreactivity remains to be investigated.

Animals↗
PubMed1978

Regulation of the immune response in autoimmune NZB/NZW F1 mice. II. Age dependent release of suppressive factors from spleen cells.

Supressor cells in the spleens of overtly autoimmune NZB X NZW (B/W) mice, but not age matched normal strain mice, were shown to release a small, less than 20,000 Dalton factor which inhibited early events in the anti-SRBC PFC response and the mitogenic response. This splenic inhibitory factor (SIF) was (i) stable on heating (56 degrees, 30 min) and freezine (-70degrees); (ii) non-specific for antigen; (iii) absorbed and/or inactivated by target cells in young B/W spleen cell cultures and (iv) released gradually into the culture medium by metabolically active cells. SIF also blocked the T-cell replacing effect of allogeneic factor (TRF) in the anti-SRBC response. These observations suggest that SIF may lead to the immunodepressed state in overtly autoimmune B/W mice by preventing the activation or differentiation of lymphocytes responding to exogenous antigen.

Aging↗
PubMed1978

Immunological senescence. I. The role of suppressor cells.

The in vitro anti-SRBC response of several murine strains declined markedly with age in parallel with an increase in the activity of suppressor cells in the spleen and bone marrow which prevented early events during the induction of the immune response. These suppressor cells released soluble mediators and lacked the characteristics of mature T cells or macrophages. In addition the suppressor cell in the bone marrow could be removed on anti-Ig columns and fractions of old splenic suppressor cells sedimenting at 0.32 cm/h were greatly enriched in surface Ig bearing cells. Old immunodepressed mice did not lack potentially immunocompetent cells since the antibody response of old spleen cells could be restored by specifically activated T cells or lipopolysaccharide which act on B cells. These results suggest that a rise in the activity of non-T suppressor cells in the spleen and bone marrow may account, in part, for the depression in humoral immunity observed in aging mice.

Aging↗