PubMed Health⌕ Search

Biomedical subjects

R K Lees

Publications and source records attributed to R K Lees.

At least 37 records · Page 2Linked to original sources
PubMed1988

Positive selection of CD4+ thymocytes controlled by MHC class II gene products.

The mature T-cell antigen receptor repertoire is characterized by lack of reactivity to self-components as well as by preferential reactivity to foreign antigens in the context of polymorphic self-proteins encoded within the major histocompatibility complex. Whereas the former characteristic (referred to as negative selection or tolerance) is associated with intrathymic deletion of T cells expressing T-cell antigen receptor beta-chain variable (V beta) domains, which confer a preferential reactivity to self antigens, the existence of the latter (referred to as positive selection or MHC restriction) has so far only been inferred indirectly from functional studies. We show here that intrathymic deletion of V+beta 6 T cells (reactive with a self-antigen encoded by the Mlsa locus) is controlled by polymorphic MHC class II determinants. Furthermore, in mice lacking expression of Mlsa, the same class II MHC loci control the frequency of occurrence of V+beta 6 cells among mature CD4+ T lymphocytes. These data are direct evidence for positive selection by MHC determinants in the thymus in unmanipulated animals.

Animals↗
PubMed1988

CD3-associated alpha/beta and gamma/delta heterodimeric receptors are expressed by distinct populations of CD4- CD8- thymocytes.

Immature double negative (DN) CD4-8- thymocytes expressing the CD3 molecular complex can be subdivided into two distinct subsets based on expression of the B2A2 antigen. Thus, B2A2+ CD3+ DN thymocytes express CD3-associated 35 kDa and 45 kDa polypeptide chains characteristic of a gamma/delta T cell receptor, whereas B2A2- DN thymocytes express predominantly 38 to 43 kDa CD3-associated structures typical of alpha/beta TCR. At the mRNA level, B2A2+ DN thymocytes express full length gamma and delta transcripts but no alpha message and only short (1 kb) B transcripts. In contrast, the B2A2- DN subset expresses full length alpha and beta transcripts and minimal levels of delta transcripts. Interestingly, B2A2- DN thymocytes, unlike mature T cells, also express abundant levels of full length TCR gamma mRNA, perhaps suggesting that these cells represent an early stage after divergence of the gamma/delta and alpha/beta T cell lineages.

Animals↗
PubMed1988

T-cell receptor V beta use predicts reactivity and tolerance to Mlsa-encoded antigens.

T lymphocytes reactive with the product of the Mlsa-allele of the minor lymphocyte stimulating (Mls) locus use a predominant T-cell receptor beta-chain variable gene segment (V beta 6). Such V beta 6-bearing T cells are selectively eliminated in the thymus of Mlsa-bearing mice, consistent with a model in which tolerance to self antigens is achieved by clonal deletion.

Animals↗
PubMed1987

Developmentally regulated expression of T cell receptor beta chain variable domains in immature thymocytes.

A minor subset of immature (CD4-,8-) thymocytes that lack expression of the B2A2 antigen was found to express low levels of surface TCR protein as detected by mAbs F23.1 and KJ16 (reacting with protein products of the V beta 8 gene family). Interestingly, F23.1/KJ16 determinants were expressed on a two- to three-fold higher proportion of B2A2- thymocytes than mature lymph node T cells in four independent haplotypes. When expanded in short-term culture with PMA and calcium ionophore, B2A2- thymocytes retained their overexpression of F23.1/KJ16 determinants and showed a fivefold elevated level (relative to lymph node) of V beta 8-specific mRNA. Taken together, these findings suggest that expression of TCR V beta genes, like Ig genes, is developmentally regulated.

Animals↗
PubMed1987

T cell antigen receptor expression in athymic (nu/nu) mice. Evidence for an oligoclonal beta chain repertoire.

The expression of T cell antigen receptors (TCR) in congenitally athymic (nude) mice has been investigated. Lymph node T cells from 4-5-mo-old athymic mice expressed full-length transcripts for the TCR alpha and beta chains at a level two-to three-fold lower than normal littermate (nu/+) controls. Low levels of expression of TCR protein at the surface of a proportion of nude T cells was demonstrated by staining with monoclonal antibodies KJ16-133 and F23.1 (directed against protein products of a family of TCR beta chain variable region genes known as V beta 8). Immunoprecipitation studies confirmed that F23.1 reacted with a similar molecular species on nude and nu/+ T cells. Studies with individual nude mice revealed a striking heterogeneity in the proportion of T cells expressing KJ16/F23.1 that was not seen in normal animals. This heterogeneity correlated with the expression of mRNA specific for V beta 8 but not with total expression of full-length beta chain transcripts. Analysis of Lyt-2+ and L3T4+ T cell subsets in individual nude mice further demonstrated that F23.1 expression was frequently associated with only one subset, and several cases were seen in which all L3T4+ cells expressed F23.1. In contrast, a similar (and constant) proportion of Lyt-2+ or L3T4+ T cells expressed F23.1 in control mice. Southern blotting of Hind III-digested DNA from nude T cells with a C beta probe revealed a more restricted pattern of TCR beta chain rearrangements than was seen for normal T cells. Taken together, these data provide compelling evidence that TCR gene rearrangement and expression can occur extrathymically. Furthermore, they suggest a model according to which the restricted functional repertoire of T cells previously observed in individual nude mice results from an oligoclonal expansion of T cells that have randomly rearranged and expressed TCR beta chain genes.

Animals↗
PubMed1987

Abnormal expression of T cell receptor genes in Lyt-2- L3T4- lymphocytes of lpr mice: comparison with normal immature thymocytes.

The autoimmunity and lymphoproliferation characteristic of lpr mice are age and thymus dependent. The accumulating Lyt-2- L3T4- T cells express only minimal cell-surface antigen receptor. After stimulation with phorbol myristic acetate (PMA) and interleukin 2, essentially normal levels of surface antigen receptor were expressed by the lpr Lyt-2- L3T4- subpopulation but remained undetectable in the corresponding normal immature thymocyte population. We have found near normal T cell receptor (TCR)-alpha and -beta mRNA expression by these lpr cells. The phenotypically comparable Lyt-2- L3T4- subset of normal thymocytes expressed approximately 10-fold less TCR-alpha mRNA than normal lymph node cells and somewhat higher TCR-beta mRNA. After cultivation of this immature thymocyte subpopulation with PMA and interleukin 2, TCR-alpha mRNA levels remained low, and TCR-beta transcripts were found to be subnormal. By using the same culture conditions, the corresponding mRNA levels of the lpr subset tended to resemble those of Lyt-2- L3T4- thymocytes. Fresh and cultured Lyt-2- L3T4- normal thymocytes showed comparably high levels of full-length TCR-gamma transcripts. In contrast, the fresh lpr subset had barely detectable levels of TCR-gamma mRNA. Upon cultivation, however, these levels increased over 200-fold to within the range observed in the Lyt-2- L3T4- thymocyte subset. No induction of the gamma gene was observed in similarly cultured normal lymph node T cells. The lpr cells may therefore correspond to an as yet undefined stage of normal T cell differentiation.

Animals↗
PubMed1985

Cell surface glycoproteins involved in the stimulation of interleukin 1-dependent interleukin 2 production by a subline of EL4 thymoma cells. I. Functional characterization by monoclonal antibodies.

Three rat monoclonal antibodies (MAb) capable of stimulating interleukin 2 (IL 2) production by a variant subline of EL4 thymoma cells (EL4-6.1) have been produced. The stimulatory capacity of these MAb (designated RL73, RL119, and RL388) was originally found to be dependent on the presence of irradiated peritoneal exudate cells; however, this requirement could be replaced by the cellfree supernatant of the "macrophage-like" cell line P388D1 or by biochemically purified human interleukin 1 (IL 1). A number of other rat MAb directed against cell surface structures did not stimulate IL 1-dependent IL 2 production by EL4-6.1 cells; however, certain MAb directed against Thy-1 as well as the lectin phytohemagglutin did have this capacity. Furthermore, the stimulatory activity of MAb RL73, RL119, and RL388 appeared to be restricted to the EL4-6.1 variant line, because neither the parental EL4 line from which it was derived nor a series of ovalbumin-specific T-T hybrids responded to these MAb. The cell surface antigens recognized by MAb RL73, RL119, and RL388 were present on a wide variety of T cell lines and T-T hybrids, as well as on lines of B cell, macrophage, and fibroblast origin. Interestingly, the MAb reacted with the majority (approximately 85%) of thymocytes but not (or only to a very small extent) with resting T lymphocytes. After stimulation by concanavalin A, however, the three MAb reacted strongly with activated T lymphoblasts. The latter data suggest that MAb RL73, RL119, and RL388 may react with cell surface structures that are normally expressed as a consequence of lymphocyte activation.

Animals↗
PubMed1985

Mutant EL-4 thymoma cells polyclonally activate murine and human B cells via direct cell interaction.

In this report we show that three mutagenized sublines of (murine) EL-4 thymoma cells can constitutively activate human and/or murine B cells via an MHC-nonrestricted cell-cell interaction. The activation signal is not by itself mitogenic but renders B cells capable of proliferating in response to interleukin 2 (IL 2). In addition, one of the mutant EL-4 sublines can constitutively respond by release of IL 2 in the presence of IL 1-containing macrophage (P388D1) supernatant. The exact relationships between these functional properties of the mutant EL-4 thymoma cells and those associated with activated normal T helper-cells remain to be established. However, the EL-4 cells provide a unique system to study in parallel murine and human B cell responses. In particular, the following observations were made during the present study. First, anti-Ig antibodies (anti-Ig) were required for B cell activation in conjunction with two EL-4 sublines acting only on murine B cells, whereas with a third subline acting on both murine and human B cells, anti-Ig was not required. Anti-Ig by itself did not lead to significant B cell activation in the absence of mutant EL-4 (or normal T) cells. Second, the growth factor-stimulated proliferation of EL-4-activated B cells, following separation of the B cells from the EL-4 cells, lasted only 2 days. These results, thus, indicate that the requirement for a surface Ig-mediated B cell activation signal depends on the quality/intensity of a direct T cell signal and that cell-cell interactions may exert a more stringent control over the growth factor responsiveness of B cells as compared with T cells.

Animals↗
PubMed1984

Frequency and specificity of precursors of interleukin 2-producing cells in nude mice.

The frequency and specificity of precursors of interleukin 2-producing cells (IL 2-P) in congenitally athymic (nude) N:NIH(s)II mice was investigated. IL 2-P were detected and quantitated in a sensitive limiting dilution microassay in which Lyt-2-depleted lymphoid cell populations were first cultured for 12 days with irradiated allogeneic (DBA/2) stimulating cells and a source of IL 2 and then washed and restimulated with irradiated T cell-depleted stimulating cells for an additional 24 hr. Supernatants from restimulated cultures were assayed for IL 2 activity on CTLL indicator cells, and IL 2-P frequencies were calculated. The results indicated that IL 2-P were undetectable in young (6-wk-old) nude mice, but increased in frequency with age to eventually reach levels five to 10-fold lower than their euthymic (nu/+) littermates. In specificity studies, microcultures established originally with limiting numbers of nude or nu/+ responding cells and DBA/2 stimulating cells were split into three aliquots and restimulated with T cell-depleted stimulating cells of DBA/2, BALB/c, or C57BL/6 origin. Analysis of IL 2 production in these restimulated microcultures clearly demonstrated different patterns of cross-reactivity in individual nude mice that were not seen in nu/+ controls. These results are discussed in the context of a model proposing that the T cell repertoire in athymic mice is oligoclonal in nature.

Aging↗
PubMed1982

Interleukin 2 production by lymphoid cells from congenitally athymic (nu/nu) mice.

The ability of lymphoid cells from congenitally athymic (nu/nu) mice to produce interleukin 2 (IL 2) was investigated. Spleen or lymph node cells (superficial or mesenteric) from nude mice on an N:NIH(S)II or BALB/c genetic background were stimulated with concanavalin A (Con A) or with irradiated allogeneic (DBA/2) spleen cells that had been depleted of T cells by treatment with monoclonal anti-Thy-1.2 antibody plus complement. After 24 hr, supernatants were harvested and assayed for their ability to support the proliferation of a cloned IL 2-dependent cytolytic T cell line. With this quantitative microassay, IL 2 production was not detectable in spleen and lymph nodes of 6-wk-old N:NIH(S)II nude mice; however, by 12 mo of age, IL 2 production increased more than 100-fold to reach levels comparable to control (nu/+) animals. Con A was more potent than alloantigen in the induction of IL 2 in either nude or control (nu/+) animals. Furthermore, differences in the genetic background of nude mice resulted in corresponding differences in both numbers of T cells (defined by monoclonal anti-Thy-1 antibody) and IL 2 production. By using negative selection with monoclonal antibodies plus complement, IL 2 production in aged nude mice was shown to depend upon a subpopulation of cells that expressed Thy-1 but not Lyt-2. These data thus demonstrate that a subpopulation of IL 2-producing cells with a Thy-1+ Lyt-2- surface phenotype can develop in the apparent absence of thymic influence.

Aging↗
PubMed1981

Age-associated increase in expression of the T cell surface markers Thy-1, Lyt-1, and Lyt-2 in congenitally athymic (nu/nu) mice: analysis by flow microfluorometry.

The expression of T cell-associated surface markers by lymphoid cells from congenitally athymic (nude) mice has been quantitatively investigated using flow microfluorometry. Spleen and lymph nodes from old (greater than 6 mo) nude mice on either a C57BL/6 or BALB/c genetic background were found to contain significant numbers (5 to 13% in spleen and 15 to 24% in lymph nodes) of cells expressing Thy-1 antigen. The proportion of Thy-1 positive cells in nude spleen was dramatically increased (to 22 to 67%) after passage of the cells over nylon wool columns. In contrast to older animals, young (1- to 2-mo-old) nude mice had undetectable levels (less than 1%) of Thy-1 bearing cells in spleen and reduced levels (6%) in lymph nodes. After passage of their spleen cells over nylon wool, some Thy-1 positive cells (10%) were detectable in 2-mo-old nude mice but none were detectable at 1 mo. In addition to Thy-1, we were able to detect the T cell alloantigens Lyt-1 and Lyt-2 on nylon wool-passed spleen cells from older C57BL/6 or BALB/c nu/nu mice. In general, the proportion of Lyt-1 bearing cells in nude lymphoid populations was similar to the proportion of Thy-1 positive cells. A smaller fraction of nude cells (corresponding to 35 to 59% of the total Thy-1 positive cells) were found to express Lyt-2. Analysis of the forward light scatter distributions of nude lymphoid cells bearing either Thy-1, Lyt-1, or Lyt-2 antigens further demonstrated that an overlapping population of relatively large-size cells expressed these surface markers. These data strongly imply that at least 2 subsets of T cells (i.e., Lyt-1+2- and Lyt-1+2+) develop in older nude mice in the apparent absence of thymic influence.

Aging↗
PubMed1981

Multicellular tumor spheroids of human colon carcinoma origin. Kinetic analysis of infiltration and in situ destruction in a xenogeneic (murine) host.

The relationship between destruction and concomitant host cell infiltration of human tumor xenografts has been quantitatively investigated by using the multicellular tumor spheroid model. Multicellular tumor spheroids of HT-29 human colon carcinoma cells were grown in vitro and subsequently implanted in the peritoneal cavity of BALB/c mice. At various times thereafter, spheroids were recovered and dissociated and their viability was quantitatively assessed by using a clonogenic assay. Little damage to spheroids was observed during the initial 4 days after implantation, but essentially complete destruction (greater than 99% reduction in clonogenic tumor cells) occurred between days 4 and 7. In parallel studies, host cell infiltration was assessed by light and electron microscopy both in situ on sections and on dissociated suspensions of spheroid cells. The data demonstrate the value of utilizing a model system in which both functional and morphological techniques can be combined in a quantitative assessment of the relationship between host cell infiltration and graft destruction in situ.

Animals↗