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M L Thoman

Publications and source records attributed to M L Thoman.

14 recordsLinked to original sources
PubMed1991

Cell proliferation and cytokine production by CD4+ cells from old mice.

Splenocytes from young adult or old C57BL/6NNia mice were stimulated in vitro with the anti-CD3 epsilon mAb, 145-2C11, in either soluble (2C11s) or plate-bound (2C11i) form. In the young group, each mode of cell activation resulted in peak DNA synthesis at approximately 48 h of culture; at this time point, the old group exhibited response levels to 2C11s or 2C11i that were approximately 40% of those in the young group. However, in the presence of 2C11i, splenocytes from old donors showed a delayed peak response which approached the peak levels attained in the young group. To analyze the responsiveness of the CD4+ T cell subpopulation, this cell type was isolated from spleens of young or old mice and was stimulated in vitro with 2C11s or 2C11i, in the presence or absence of added accessory cells (T cell-depleted, irradiated splenocytes). The induction of DNA synthesis by 2C11s was accessory cell dependent, and the response in the old group were markedly reduced in comparison to those in the young group. In contrast, stimulation of DNA synthesis with 2C11i was relatively accessory cell independent, resulted in higher response levels in both age groups, and lessened the disparity between age groups. The analysis of IL-2 and IL-4 secretion by stimulated CD4+ cells revealed that, in response to 2C11s and accessory cells, only IL-2 accumulation was detectable and the levels in the young group were approximately 10-fold higher than the IL-2 levels in the old group. However, stimulation of CD4+ cells with 2C11i and accessory cells yielded improved IL-2 production and a detectable IL-4 response in the old group, whereas the young group exhibited a response profile similar to that induced by 2C11s. Further analysis of the IL-2, IL-4, and IFN gamma mRNA levels in 2C11i-stimulated CD4+ cells revealed that old donor cells accumulated similar levels of IL-2 transcripts, but higher levels of IL-4 and IFN gamma transcripts, than young donor CD4+ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1991

Impaired responsiveness of IL-2 receptor-expressing T lymphocytes from aged mice.

IL-2 receptor-bearing splenic T lymphocytes derived from aged C57BL6/J mice (22-24 months) display a relative inability to respond to IL-2 when compared to similar cells from young (2-3 months) animals. As a population the aged cells incorporate less [3H]thymidine and fewer are able to undergo vigorous clonal growth. Both the CD4+ and CD8+ subsets display these defects. The clonal assay indicates that aged T cells, in addition to having longer cell cycle transit time, also have a higher frequency of cell cycle arrest than similarly activated young T cells. This defect in IL-2 responsiveness is distinct from those in early signal transduction which limit aged T lymphocyte entry into cycle and cannot be corrected by phorbol myristate acetate or ionomycin.

Aging↗
PubMed1990

Induction of human B cell differentiation by Fc region activators. II. Stimulation of IL-6 production.

Fc region fragments derived from the enzymatic cleavage of human IgG have been shown to induce human peripheral blood-derived B cells to differentiate into Ig secreting cells (ISC). The synthetic peptide p23, corresponding to residues 335 to 357 in the Fc region of human IgG1, represents a region of the molecule responsible for stimulation of ISC formation. Fc region-induced ISC formation requires at least two signals; one supplied by Fc region activators and one supplied by a T cell-derived factor(s). In this report we show that the coculture of human PBMC with pFc' or p23, results in the release of factor(s) that resemble IL-6 in its pattern of biologic activity. This conclusion is based on the observations that supernatants from Fc region-stimulated PBMC cultures contained increased levels of elements that scored as positive in two assays for IL-6: the B9.9 hybridoma growth and the CESS cell differentiation assays. Moreover, RNA from Fc region-stimulation PBMC contained increased levels of IL-6 cDNA-hybridizable elements. Finally, it was observed that rabbit anti-IL-6 inhibited the ability of supernatants derived from Fc region-stimulated PBMC cultures to induce B9.9 cell proliferation as well as p23-induced ISC formation in intact PBMC cultures. Fc region fragments induce both monocytes and T cells to produce IL-6. Taken together, these results indicate that IL-6 is produced in Fc region-stimulated PBMC cultures and is involved in B cell activation by these activators.

Adult↗
PubMed1988

The effect of aging on the induction of tolerance in a subpopulation of B lymphocytes.

The present data further demonstrate that a subpopulation of B cells which were functionally deleted during aging can be revived in vivo with 7m8oGuo. This compound is a member of a family of derivatized ribonucleosides which are potent B-cell activators and adjuvants. Using this compound as a probe to revive aged hyporesponsive B cells of CBA/CaJ mice, it was demonstrated that a subpopulation of B cells functionally deleted by the aging process can be readily tolerized by DHGG in that they fail to respond to AHGG in the presence of 7m8oGuo. It appears that this compound directly affects the B cells, since it has previously been shown that another derivatized nucleoside with identical lymphocyte-modulating properties has no effect on Th cells once they have been tolerized to DHGG. B cells stimulated by the combined effect of AHGG and 7m8oGuo were more readily tolerized in aged than in young adult mice.

Aging↗
PubMed1988

Partial restoration of Con A-induced proliferation, IL-2 receptor expression, and IL-2 synthesis in aged murine lymphocytes by phorbol myristate acetate and ionomycin.

The activation by concanavalin A (Con A) of murine lymphocytes derived from aged animals is impaired, as demonstrated by lower IL-2 synthesis, display of fewer IL-2 receptors, and less [3H]thymidine incorporation relative to similarly treated cells from young animals. The ability of the phorbol ester, phorbol 12-myristate 13-acetate (PMA), and the calcium ionophore, ionomycin, in conjunction with Con A, to improve these parameters of activation has been assessed. When splenic lymphocytes derived from aged mice are cultured with Con A plus ionomycin, IL-2 synthesis and IL-2 receptor expression are increased over the values obtained in parallel cultures triggered by Con A alone up to levels equal to that obtained in Con A-activated young cultures. The proliferative response is less sensitive to the augmenting effect of ionomycin. PMA is much less effective in improving these parameters of Con A activation. PMA plus ionomycin, in the absence of Con A, triggers cell cycle transition of lymphocytes derived from both aged and young animals. Both IL-2 synthesis and IL-2 receptor expression induced by PMA plus ionomycin reach levels equal or near equal that found in parallel cultures of cells from young animals; however, proliferation is lower than in young adult cultures.

Animals↗
PubMed1987

Augmentation of the antibody response in aged mice with an 8-derivatized guanosine nucleoside and its effect on immunological memory.

The injection of aged mice with 7-methyl-8-oxoguanosine (7m8oGuo) along with aggregated human gamma-globulin (AHGG) results in an enhanced anti-HGG antibody response. Aged mice injected with AHGG alone make only a feeble anti-HGG response. The enhanced response in aged mice was not significantly different from the response obtained in young-adult mice injected only with AHGG. However, the enhanced response obtained by injection of 7m8oGuo in young-adult mice was several orders of magnitude greater than that observed in the aged mice. Aged mice given a primary injection of AHGG alone failed to make a secondary response to AHGG given 90 days later, whereas aged mice injected with 7m8oGuo along with a primary injection of AHGG showed variable secondary antibody responses to AHGG. Two of seven mice showed high degrees of immunological memory equivalent to that seen in young-adult mice while others showed either meagre or no responses. The effect of 7m8oGuo appeared to be primarily on B cells, albeit the role of T cells cannot be ruled out.

Aging↗
PubMed1987

Identification of a lymphocyte-activating pentapeptide sequence in the Fc region of human IgG1.

The synthetic peptide p23, representing residues 335 to 357 in the Fc region of human IgG1, was previously shown to induce Ig secretion in murine spleen cell cultures. In this report, overlapping peptides based on the sequence of p23 were synthesized to further map the active site in this molecule. The results from these studies indicate that leu-pro-pro-ser-arg (residues 351 to 355) retained the B cell differentiation-inducing properties of p23; however, expression of activity by this sequence was markedly influenced by N-flanking sequences. By using T cell-depleted spleen cell cultures, it was determined that at least two signals are required for p23-induced Ig secretion: one supplied by p23 directly and one supplied by a T cell-replacing factor present in p23-conditioned spleen cell supernatants. Both signals were mapped into the sequence leu-pro-pro-ser-arg. However, the latter signal, but not the former signal, again appeared to be influenced by sequences proximal to the active site. These data indicate that although the leu-pro-pro-ser-arg sequence is able to provide both required signals for p23-induced Ig secretion in spleen cell cultures, there may be subtle differences in how the cell types involved in this response interact with and/or are activated by this sequence.

Amino Acid Sequence↗
PubMed1987

Retention of T cell reactivity to mitogens and alloantigens by Peyer's patch cells of aged mice.

Immune function generally declines with advancing age. However, recent evidence suggests that this decline may differentially affect the lymphoid compartments comprising the immune system. The effect of age on the T cell-mediated competency of cells from two different lymphoid compartments, Peyer's patch (PP) and spleen, was studied. PP cells of aged C57BL/6 mice retained a greater capacity to proliferate in response to concanavalin A, phytohemagglutinin, and alloantigen and to generate alloimmune cytotoxic cells than did splenocytes of aged mice when compared with their young counterparts. These results could not be explained by significant shifts in the response kinetics or in the proportions of T cells in individual tissues. These results support the concept that lymphoid compartments are not equally sensitive to the deleterious effects of the aging process.

Aging↗
PubMed1985

Human C3a-mediated suppression of the immune response. II. Suppression of human in vitro polyclonal antibody responses occurs through the generation of nonspecific OKT8+ suppressor T cells.

C3a-mediated suppression of Ig secretion in human PBL cultures occurs through the activation of suppressor T cells. Incubation of T cell-enriched populations derived from peripheral blood or tonsil results in the activation of nonspecific OKT3+8+ suppressor T cells capable of inhibiting Fc fragment-induced Ig secretion in fresh autologous PBL cultures. Generation of OKT8+ suppressor T cells by C3a requires the interaction of T cells, adherent cells, and C3a. Activation of the suppressor-T-cell pathway is initiated early in culture. Incubation of the T-cell-enriched populations with C3a for 0.5 hr results in functional, transferable suppressor cells. Maximum suppression was achieved when C3a was allowed to interact with the cell population for 1-2 hr.

Antibody Formation↗
PubMed1985

Bioactive complement fragments in immunoregulation.

Several fragments derived from complement components have been identified as potent effector substances in in vitro assays that measure cell proliferation and antibody synthesis. The anaphylatoxin C3a suppresses the immune response but fails to influence T- or B-cell proliferation. The factor C5a augments both antibody production and antigen-induced, but not mitogen-induced, T-cell proliferation. C3a-mediated suppression occurs through the activation of a suppressor T-cell cascade with macrophage collaboration. C5a-mediated enhancement, depending upon the in vitro system studied, acts at the level of the helper T cell and/or macrophage. A fragment generated from treating iC3b with kallikrein (c3d-K) has aided in defining a structural region of the C3b molecule that can influence the level of circulating leukocytes. The factor C3d-K is also capable of suppressing both specific and non-specific T-cell proliferative responses and mitogen-induced B cell growth. The mechanism of C3d-K action is defined as a direct effect on "activated" T cells, even though IL-2 synthesis of treated cells is diminished. The effect of C3d-K is long lasting, non-reversible and requires only a short exposure to the target cell.

Animals↗
PubMed1985

Human C3a-mediated suppression of the immune response. I. Suppression of murine in vitro antibody responses occurs through the generation of nonspecific Lyt-2+ suppressor T cell.

C3a derived from the third component of human complement was found to suppress in vitro murine anti-SRBC responses. C3a-mediated suppression occurs through the generation of nonspecific Lyt-2+ suppressor T cells. The generation of suppressor cells occurs at an early phase in the response because incubation of naive T cells with C3a for as little as 30 min results in suppression of the anti-SRBC response. The generation of suppressor T cells requires the interaction of T cells, C3a, and a Sephadex G-10-adherent cell, presumably a macrophage. Although the mechanism of action of these suppressor cells has not been elucidated, several possibilities have been eliminated. C3a-suppressor T cells do not apparently release inhibitory lymphokines, nor is helper cell activity inhibited by a 2-day co-culture with these suppressor cells. The observation that interleukin 2 (IL 2)-containing lymphokine preparations could overcome C3a-induced suppression led us to investigate the interaction of the suppressors with IL 2 producer cells. However, neither C3a nor C3a-generated suppressor T cells can block the synthesis of IL 2.

Animals↗
PubMed1985

Reconstitution of in vivo cell-mediated lympholysis responses in aged mice with interleukin 2.

Advancing age is accompanied by declining immune potential. Both humoral and cellular immune responses are diminished in aged humans and experimental animals. A major lesion preventing effective T cell-mediated responses is the lack of interleukin 2 (IL 2) synthesis in aged mice. Addition of IL 2 can effectively reconstitute in vitro T cell-dependent humoral and cell-mediated immunity. These results have been extended, demonstrating that IL 2-containing lymphokine preparations when administered with antigen can restore the ability of aged mice to generate cytotoxic T lymphocytes in vivo. Furthermore, IL 2 has been identified as the active component of these lymphokine preparations through the use of purified human IL 2 prepared by recombinant DNA and gene cloning technology. The cloned IL 2 is highly effective in enhancing the immune responses of aged animals both in vitro and in vivo.

Aging↗