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M F Wilkinson

Publications and source records attributed to M F Wilkinson.

65 records · Page 4Linked to original sources
PubMed1988

Induction of T-cell receptor-alpha and -beta mRNA in SL12 cells can occur by transcriptional and post-transcriptional mechanisms.

Genes encoding the alpha and beta subunits of the T-cell receptor (TCR) for antigen require rearrangement events for functional expression. In the case of the immunoglobin genes, rearrangement events have been shown to be necessary, but they are not sufficient for full gene expression. The regulation of TCR genes, apart from the requirement for rearrangement, remains to be elucidated. The T-lymphoma cell clone SL12.4 actively transcribes both TCR-alpha and -beta genes and the cells contain nuclear TCR precursor transcripts. However, the cells fail to accumulate appreciable quantities of mature TCR-alpha and -beta mRNAs in either the nucleus or the cytoplasm. The protein synthesis inhibitor cycloheximide (CHX) induces a 20-fold increase in mature TCR-alpha transcript accumulation without a concomitant increase in TCR-alpha gene transcription suggesting that CHX reverses the nuclear post-transcriptional events which prevent mature TCR-alpha mRNA accumulation. CHX also induces full length TCR-beta transcripts greater than 90-fold while TCR-beta gene transcription increases only 2- to 4-fold. The calcium ionophore A23187 induces the accumulation of TCR-alpha but not -beta transcripts; and in contrast to CHX, it increases the rate of TCR-alpha gene transcription and the expression of large nuclear TCR-alpha precursor transcripts. Since CHX and A23187 mediated induction of TCR mRNA is both rapid and reversible, it is unlikely that new DNA rearrangements are responsible for the induction. Collectively, the data show that the accumulation of mature TCR-alpha and -beta transcripts in SL12.4 cells can be coordinately or independently induced by nuclear events involving both transcriptional and posttranscriptional mechanisms.

Animals↗
PubMed1987

The antipyretic effects of centrally administered vasopressin at different ambient temperatures.

The antipyretic response to arginine vasopressin (AVP) was investigated at 3 ambient temperatures using unanesthetized freely behaving male rats. Responses of non-febrile and febrile rats to intracerebroventricular (i.c.v.) injections of AVP and s.c. injection of indomethacin were observed at cold (4 degrees C), thermoneutral (25 degrees C) and warm (32 degrees C) ambient temperatures. In agreement with previous reports i.c.v. AVP at 25 degrees C decreased brain temperature of febrile but not non-febrile rats. This antipyretic effect was also observed at the warm ambient temperature and during cold exposure. Responses to s.c. indomethacin were qualitatively similar to i.c.v. AVP at neutral and warm temperatures. In the cold, however, indomethacin decreased the brain temperature of both non-febrile and febrile animals, although unlike AVP, brain temperature of non-febrile animals were decreased somewhat more than that of febrile animals. These data show that AVP decreases brain temperature of febrile more than non-febrile rats at all ambient temperatures and may therefore be acting partially on febrile set point. It is likewise clear that AVP affects specific effector mechanisms since antipyretic effects were of different magnitudes at different ambient temperatures. The observation that AVP and indomethacin have qualitatively similar effects on fever at the 3 ambient temperatures suggest that they may act via a common neural pathway.

Animals↗
PubMed1987

Antipyresis due to centrally administered vasopressin differentially alters thermoregulatory effectors depending on the ambient temperature.

The intracerebroventricular (i.c.v.) administration of arginine vasopressin (AVP), in the febrile rat elicits an antipyresis at cold, warm and neutral ambient temperatures. These experiments were conducted, therefore, to elucidate the thermoregulatory effector mechanisms responsible for this antipyretic effect. At 25 degrees C, AVP-induced antipyresis was mediated by tail skin vasodilation while metabolic rate was unaffected. At 4 degrees C, the antipyresis produced by AVP was approximately double that seen at 25 degrees C. This effect appeared to be mediated exclusively by inhibition of heat production since the metabolic rate decreased markedly following AVP. This antipyresis at 4 degrees C was accompanied by cutaneous vasoconstriction. At 32 degrees C, neither vasomotor tone, metabolic rate nor evaporative heat loss could be shown to contribute to the small antipyretic effect elicited by AVP. We conclude from these data that i.c.v. AVP is producing antipyresis by affecting the febrile body temperature set-point mechanism since the thermoregulatory strategy to lose heat varies at different ambient temperatures and the decrease in body temperature cannot be shown to be due to changes in a single effector mechanism.

Animals↗
PubMed1987

Vasopressin functions as an endogenous antipyretic in the newborn.

These experiments sought to determine the role of arginine vasopressin (AVP) in the inability of newborns to produce a fever. Our data demonstrate that the AVP analog, [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid)-2-(O-methyl) tyrosine]arginine vasopressin (M-AVP), administered centrally to adult rats, prevented the antipyretic action of centrally injected AVP. Behaviorally thermoregulating 3-day-old rat pups failed to respond to endoxin with a fever, similar to neonates of other species, but when central AVP antipyretic receptors were blocked by pretreatment with M-AVP, the pups were able to raise their body temperature to febrile levels. The antipyretic drug, indomethacin, prevented these fevers. We conclude that endogenous AVP is a physiologically important antipyretic substance in the brain of the newborn rat.

Animals↗
PubMed1986

Gamma-interferon production by human low-density lymphocytes induced by T-cell mitogens.

Low-density lymphocytes prepared by Percoll fractionation of human peripheral blood mononuclear leucocytes were found to produce large amounts of interferon-gamma (IFN-gamma) in response to different T-cell mitogens in the absence of macrophages, whilst higher density lymphocytes were strongly dependent on the presence of macrophages for significant IFN-gamma production. The addition of macrophages to the low-density lymphocytes made little difference to their IFN-gamma production. Subsets of the low-density lymphocytes prepared by rosetting with sheep red blood cells produced markedly less IFN-gamma than did the original population; IFN-gamma production could be largely restored by recombining the two low-density fractions. This suggests that IFN-gamma production by low-density lymphocytes whilst macrophage-independent does require co-operation between different cell types. The low-density lymphocytes were enriched for cells bearing the Leu 11 and OKM1 antigens, and for natural killer cell activity. The rosetting fraction was enriched for OKT3 antigen-bearing cells, and the non-rosetting fraction was enriched for Leu 11, OKM1 antigen-bearing cells. Depletion of B cells (surface Ig-positive) by nylon-wool chromatography had no effect on IFN-gamma production by low-density lymphocytes.

Concanavalin A↗
PubMed1985

Interleukin 2 receptor blockade by anti-Tac antibody inhibits IFN-gamma induction.

Anti-Tac antibody, which binds to the interleukin 2 (IL-2) receptor and thus blocks IL-2 binding to and activation of T lymphocytes, was used to investigate the role of IL-2 in interferon-gamma (IFN-gamma) production. Three T-cell mitogens (phytohemagglutinin, concanavalin A, and the pan-T monoclonal antibody OKT3) were used as IFN-gamma inducers. In each case, anti-Tac antibody clearly inhibited IFN-gamma production. This occurred even under conditions where cellular proliferation (as measured by incorporation of [3H]thymidine) was only slightly inhibited. The inhibitory effects of anti-Tac were reversed by the addition of purified IL-2. Therefore, endogenous production of IL-2 and its binding to the IL-2 receptor are needed for maximum IFN-gamma production.

Antibodies, Monoclonal↗
PubMed1984

Differences in the expression of the human interferon-gamma gene in fresh lymphocytes and cultured lymphoblasts.

Fresh human peripheral blood mononuclear lymphocytes and lymphoblasts that had been grown for a period in T-cell growth-factor containing medium were stimulated with staphylococcal enterotoxin A plus mezerein to produce interferon-gamma (IFN-gamma). Growing lymphoblasts produced peak levels of IFN-gamma much earlier after induction than fresh lymphocytes. Quantitation of the steady-state levels of IFN-gamma mRNA showed these to differ markedly between the two cell types over a period of time post-induction. In fresh lymphocytes the steady-state levels of IFN-gamma mRNA increased to a peak level over a period of 4 days while in growing lymphoblasts the peak level occurred after 8 hours. These differences in IFN-gamma mRNA production were shown to be not the result of gross alteration of RNA metabolism following blast transformation.

Cells, Cultured↗
PubMed1984

Gamma-interferon induction in human lymphoblasts compared with fresh mononuclear leucocytes: earlier synthesis, rapid shut-off and enhancement of yields by metabolic inhibitors.

The mechanisms of gamma-interferon (IFN-gamma) induction in fresh human peripheral blood mononuclear leucocytes (PBML) and proliferating lymphoblasts were compared. Cotreatment with mitogen (Staphylococcal enterotoxin A) and tumour promoter (mezerein) was used to induce maximum IFN-gamma production and thus to study the induction process under optimum conditions. Total IFN yields were about the same from both cell types. Proliferating lymphocytes produced IFN much earlier and more transiently than fresh PBML. Experiments with actinomycin D indicated that de novo synthesis of RNA was required for IFN-gamma production in both PBML and lymphoblasts, but that for maximal IFN-gamma production, lymphoblasts required RNA synthesis for a shorter period (1 hr) after induction than did fresh PBML (greater than 15 hr). Appropriate schedules of treatment with metabolic inhibitors actually increased IFN production in lymphoblasts. This 'superinduction' could not be demonstrated for fresh PBML, implying differences in the turn-off of IFN-gamma production in these two cell types. Taken together, these results indicate that IFN-gamma expression is regulated differently in quiescent and activated lymphocytes.

Dactinomycin↗
PubMedDate not supplied

A model system for T-lymphocyte differentiation: regulation of CD4 and CD8 gene expression in SL12.4 T-lymphoma cell clones.

The T-cell surface proteins CD4 (L3T4) and CD8 (Lyt2) are first expressed on thymocytes as they undergo maturation in the thymus. Two immature T-lymphoma cell clones SL12.4 and RS4.2 which constitutively express low or undetectable levels of CD4 and CD8 were used to investigate the activation of CD4 and CD8 gene expression. The protein synthesis inhibitors cycloheximide (CHX) and pactamycin rapidly and reversibly increased CD4 and CD8 mRNA in the cloned cell lines, suggesting that a labile inhibitor protein(s) may regulate the expression of these transcripts. Cell surface CD4 and CD8 proteins were transiently detectable following a pulse of CHX. Thymic epithelial cell lines also induced CD4 and CD8 mRNA and cell surface protein, as well as TCR-alpha mRNA when co-cultivated with SL12.4 T lymphoma cells. The increase in CD4 and CD8 was modest, but stable for at least 22 cell generations after the thymic epithelial inducer cells were removed. Epithelial cells of non-thymic origin did not cause induction of these T-cell differentiation markers in SL12.4 T-lymphoma cells. Since the induction elicited by thymic epithelial cells and protein synthesis inhibitors differed dramatically in kinetics and reversibility, it is likely that these inducers act, at least in part, via different mechanisms. This lymphoma model system may be useful for analysis of molecular events which occur in immature thymocytes undergoing differentiation.

Animals↗
PubMedDate not supplied

Androgen regulation of the Pem homeodomain gene in mice and rat Sertoli and epididymal cells.

Although the role of homeodomain transcription factors during embryogenesis is well known, their developmental function in postnatal animals is only beginning to be understood. We examined the regulation and expression pattern of Pem, a homeodomain protein that may regulate androgen-dependent events in the testis and epididymis. Immunohistochemical analysis showed that Pem protein is expressed selectively in the nuclei of Sertoli cells during the androgen-dependent stage of the seminiferous epithelium cycle in vivo. RNase protection analysis revealed that a proximal promoter was responsible for androgen-dependent mouse Pem expression in testis and epididymis in vivo, whereas a distal promoter was used in placenta. The mouse Pem gene was expressed at approximately 10-fold higher levels in the testis than in the epididymis; conversely, the rat Pem gene was expressed at >10-fold higher levels in the epididymis than in the testis. Because androgen-binding protein has been proposed to transport androgens from the testis to the epididymis, we tested whether the > or = 20-fold higher levels of androgen-binding protein expression in the rat, compared to that of mouse, are responsible for the differential expression of Pem in these two rodent species. Studies with androgen-binding protein transgenic mice demonstrated that the species-specific difference in androgen-binding protein expression is unlikely to be responsible for the species-specific difference in Pem expression. We found that androgen is necessary but not sufficient for Pem expression, since purified Sertoli cells rapidly down-regulated Pem transcripts in culture, regardless of the presence of testosterone. We conclude that Pem gene expression in Sertoli cells requires other cell types or cellular factors in addition to androgen.

Androgen-Binding Protein↗