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Biomedical subjects

R B Colvin

Publications and source records attributed to R B Colvin.

At least 127 records · Page 7Linked to original sources
PubMed1990

Modulation of expression of MHC antigens in the kidneys of mice by murine interferon-alpha/beta.

We have analyzed the effects of interferon-alpha/beta on MHC expression in the murine kidney, and compared these results with the MHC modulating effects of interferon-gamma. Natural murine interferon-alpha/beta was administered to B10.BR mice (H-2k), i.p., twice daily for 3 days. Expression of MHC antigens was assessed on day 4 by immunoperoxidase staining with biotinylated monoclonal antibodies to class I (KkDk) and class II (I-Ak) antigens. Interferon-alpha/beta significantly decreased the number of class II-positive renal cortical dendritic cells from 62.0/mm2 to 12.6/mm2 (P less than 0.001). A similar but less dramatic decrease was seen in cardiac dendritic cells. Little or no change in class II expression was observed in proximal tubules or glomeruli. Interferon-alpha/beta induced marked class I staining in the glomerulus, arterial endothelium, and Bowman's capsule. Proximal tubule cells also showed increased class I expression, but were less responsive than glomeruli. Thus, the effects of interferon-alpha/beta contrast with those of interferon-gamma, which increases class II expression on proximal tubules, induces relatively more class I expression in proximal tubules than glomeruli, and increases class II-positive dendritic cells. Furthermore, these results suggest that treatment with interferon-alpha/beta may have a complex effect on the immune response to a renal allograft due to its differential effects on class I and class II cell surface expression.

Animals↗
PubMed1990

Immunogenic epitopes of the p55 chain of the IL-2 receptor. Relationships to high-affinity IL-2 binding and modulation of the p55 chain.

Monoclonal antibodies were used to determine the relationships between epitopes on the p55 chain of the IL-2 receptor and high-affinity IL-2 binding. Five monoclonal antibodies to the human P55 chain of the IL-2 receptor were induced by immunizing mice with murine L cells that were transfected with human p55 cDNA. Since the p55 chain is the only human antigen expressed on these cells, all antihuman MABs thus generated were directed against this molecule. These antibodies were used to map epitopes on the p55 chain and determine their relationship to high-affinity IL-2 binding. Extensive flow cytometric studies with these MABs and a large panel of other anti-p55 MABs revealed three major patterns of competition. Type I MABs compete with anti-Tac extensively but not with antibodies of other groups. Type II MABs do not block anti-Tac but do block 7E11. Type III MABs do not block either type I or type II antibodies. 125I-IL2 competition studies under high-affinity conditions revealed that types I and II MABs inhibit IL-2 binding. Type III MABs can be resolved into two subgroups, one that inhibits IL-2 binding and one that does not. Together these data suggest that there are at least four distinct immunogenic epitopes on the human p55 chain, with three epitopes related to IL-2 binding. The competitive component evident by a change in Kd on the Scatchard plots suggests that all three epitopes are close to or part of the IL-2-binding site of the p55 chain. The noncompetitive component, as evidenced by the lower number of high-affinity IL-2 receptors induced by these antibodies, suggests that the same epitopes are also close to the site(s) of interaction between the p55 and p70 chains to form the high-affinity receptor. These studies indicated that the IL-2-binding site and site of interaction between the p55 and p70 chains are close together or identical. Modulation studies revealed that one type II antibody (7E11) modulates the p55 chain in the absence of IL2 and the p70 chain, thus revealing that modulation of the p55 chain can occur by an active process, and not merely passively comodulate by the p70 chain upon IL-2 binding. Modulation of the p55 chain alone has no proliferative effect on IL-2-responsive T lymphoblasts. Potentially this antibody-dependent modulation may be used to deliver toxin to activated lymphocytes.

Antibodies, Monoclonal↗
PubMed1990

The mechanism of anti-CD3 monoclonal antibodies. Mediation of cytolysis by inter-T cell bridging.

OKT3, an anti-CD3 MAB, depletes T cells in vivo and is among the most potent inhibitors of acute allograft rejection. The mechanism of this inhibition is unknown. The present studies investigate whether anti-CD3 antibodies have the ability to crosslink CD3 on two different cells and induce TCR-dependent antibody-bridged cell-mediated cytolysis (TCR-ABCMC) between T cells. Two different anti-CD3 antibodies (OKT3 and CD3,3) and OKT3 F(ab')2 were all highly effective in inducing cytolysis of CD8+ and CD4+ T cells by CD8+ T cells, and CD8+ T cells by CD4+ T cells. Monovalent OKT3 Fab was 25-125-fold less potent than OKT3 F(ab')2. Monovalent CD3,X was totally ineffective. The necessity for intercellular bridging was evidenced by the observation that an anti-CD3:anti-CD4 (CD3,4) bispecific MAB (BSMAB) was effective in mediating lysis of CD4+ but not CD8+ T cells by CD8+ T cells. These studies indicate that neither FcR-mediated ADCC nor complement fixation is necessary for bivalent anti-CD3 MAB to lyse T cells. Inter-T cell TCR-ABCMC may be particularly effective in inflammatory tissues, such as rejecting allografts and autoimmune diseases, in which numerous cytolytic T lymphocytes are present in close association with other T cells.

Animals↗
PubMed1990

Prolonged survival of nonhuman primate renal allograft recipients treated only with anti-CD4 monoclonal antibody.

The immunosuppressive efficacy of the monoclonal antibody OKT4A reactive with human and monkey CD4 cells was evaluated in cynomolgus renal allograft recipients. Low-dose (0.1 to 0.3 mg/kg/day) intact monoclonal antibodies (10 recipients) or F(ab')2 fragments (two recipients) were administered for 12 days. High-dose OKT4A (10 mg/kg) was administered on the day of transplantation as the only suppression in five animals. Four control animals received either no therapy or a monoclonal antibody nonreactive with monkey cells (OKT3). Maximum survival of the control animals and those treated with F(ab')2 was 11 days. Mean survival in the recipients of low-dose OKT4A was 25.4 +/- 4.3 days and in the group receiving high-dose OKT4A it was 39 +/- 6.4 days. All OKT4A-treated animals showed "coating" and CD4 modulation without depletion of circulating T cells. No modulation occurred in the F(ab')2-treated recipients. Serial allograft biopsy specimens showed reduced lymphocyte infiltration that was nearly complete in recipients of high-dose OKT4A. Biopsy-derived donor-reactive cytotoxic T-cell lines were generated regularly from recipients of low-dose, but not high-dose, OKT4A during periods of stable function. All animals treated with monoclonal antibodies developed an immunoglobulin G antimurine humoral response. Thus OKT4A is a potent immunosuppressive agent administered even as a single bolus, and depletion of CD4 cells is not required to suppress rejection. Anti-CD4 monoclonal antibodies may prove useful in patients, perhaps requiring only a limited number of higher-dose injections in the peritransplant period.

Animals↗
PubMed1989

Identification of pre-T cells in human peripheral blood. Extrathymic differentiation of CD7+CD3- cells into CD3+ gamma/delta+ or alpha/beta+ T cells.

CD7+CD3- cells purified (greater than 99.99%) by FACS from the peripheral blood of healthy adults include precursors for mature T cells that have the capacity to differentiate into TCR-1+ or TCR-2+ CD3+ cells. Extrathymic differentiation was demonstrable from all eight healthy donors in the presence of a high concentration of IL-2, mitogenic levels of PHA, and irradiated blood mononuclear feeder cells, after a lag of approximately 40 d in vitro. The extrathymic T (ET) cells were predominantly TCR-1+, although TCR-2+ cells were also derived. ET TCR-1+ cells were CD4-CD8-, CD4-CD8DIM+, and CD4+CD8-, and were distinguished from natural T TCR-2+ cells by a variety of cell surface markers. The ET cells had phenotypes generally displayed by normal mature T cells, although the CD5DIM+ on ET cells was more typical of thymocytes. Acquisition of CD3 on purified CD7+CD3- cells was not due to antigenic modulation or growth of contaminants, and ET cells could be demonstrated at the clonal level. Studies in athymic mice and bone marrow recipients support the view that extrathymic maturation does occur in vivo. Whether the CD7+CD3- cell population was unexposed to the thymus, or exposed but not processed, is unknown. In any case, unusual or "forbidden" autoreactive specificities are predicted since ET cells differentiate without thymic selection of the TCR.

Antigens, CD7↗
PubMed1989

Fibronectin and corneal epithelial wound healing in the vitamin A-deficient rat.

The time course of the appearance of fibronectin (Fn) on wounded corneal surfaces was studied in vitamin A-deficient (A-) and pair-fed control rats. At various times following a central epithelial abrasion, the tissue was harvested, and Fn was localized on frozen corneal sections by an indirect immunofluorescence technique. There was no detectable Fn in intact, nonwounded control or intact A-corneas, except for Descemet's membrane. Within a half hour after abrasion, a band of Fn appeared on the denuded corneal surface of pair-fed control rats and became a continuous, prominent layer at four hours. This layer remained until 16 hours but disappeared at 24 hours when the epithelium had resurfaced over the defect. In severely A- rats, reepithelialization following central epithelial abrasion was delayed, and no Fn band was discernible at any time from one to 32 hours after injury. Light microscopy revealed a progressive increase in polymorphonuclear neutrophil infiltration with time in the underlying stroma in severely A- rats. This study indicated that in severe vitamin A deficiency, delayed epithelial migration is associated with an inflammatory cell layer and occurred in the absence of Fn.

Animals↗
PubMed1989

Variation in patient response associated with different preparations of murine monoclonal antibody therapy.

The sera of 37 renal and 12 liver allograft recipients treated with OKT3 (42), Leu2a (7), or both (2) monoclonal antibodies were serially analyzed by an enzyme-linked immunosorbent assay to determine the humoral response (IgG) to mAb. Anti-mAb IgG to the treatment mAb was detected in the serum of 23 (76%) renal and 6 (50%) liver OKT3 recipients, and all 7 Leu2a renal recipients, usually within 14 days of mAb completion, but never during the first week of Rx. Each of the 7 Leu2a recipients developed reactivity not only to Leu2a isotype (IgG1), but also to OKT3 isotype (IgG2a). In contrast, only 1 of the 42 renal and liver allograft recipients treated with OKT3 developed reactivity to the Leu2a isotype. Blocking studies indicated that the specificity of the response to the treatment mAb was directed at the idiotype--and, in some patients, to the constant domain (isotype) of the mAb administered. The antibody response to an alternate isotype (IgG2a) observed in Leu2a (IgG1)-treated patients most likely resulted from irrelevant immunoglobulin (IgG2a) in the Leu2a preparation. This reactivity appeared to be specific for the IgG2a subclass. Clinicians administering mAb therapy should be aware that various mAb preparations may contain immunoglobulin isotypes unrelated to the therapeutic mAb. Crossimmunization to the irrelevant immunoglobulins may occur, precluding subsequent use of other mAbs sharing similar isotype.

Antibodies, Anti-Idiotypic↗
PubMed1989

Function and surface phenotype of T lymphocytes infiltrating renal allografts in nonhuman primates treated with monoclonal antibodies.

The phenotype and function of T lymphocyte cell lines established in vitro from kidney biopsies at the time of acute cellular rejection were studied using a nonhuman primate renal allograft model. Our objectives were to investigate the function and surface phenotype of cells that infiltrate renal allografts in animals that were untreated, that were given subtherapeutic cyclosporin, or that developed rejection after treatment with monoclonal antibodies to IL-2R B chain (CD25), immune cell adhesion molecule-1 (ICAM-1), or CD8. Lines from allograft biopsies and peripheral blood were expanded in vitro using solely human recombinant IL-2 and analyzed after 6-20 days in culture. We found that the large majority of cells cultured from cynomolgus allografts at the time of acute rejection or, when possible, assayed directly without culture, were CD3+4-8+ T lymphoblasts that possessed donor-specific cytolytic function and an NK-line, cytotoxic activity. In contrast, it was rarely possible to establish T cell lines exhibiting donor-specific cytotoxic activity from the blood except in the absence of immunosuppression or during CsA taper. A stable number of graft-derived CD4+8- cells was only observed in an unsuppressed animal 2 days after transplantation in the absence of manifest signs of rejection. Taken together, the above data indicate that similar T lymphocyte populations associated with allograft rejection are present in acutely rejecting allografts after the various types of immunosuppressive therapy. Since the infiltrating cells were similar to those obtained prior to therapy, recurrent rejection most likely represents cells that have escaped elimination. The T cells derived from monkey grafts differ from those from human renal allografts by the decreased frequency of CD4+ cells. Whether this difference is species-related or therapy-related is not known.

Animals↗
PubMed1989

A critical analysis of serum and urine interleukin-2 receptor assays in renal allograft recipients.

A component of the interleukin 2 receptor (IL-2R) is released in soluble form during T cell activation and can be detected in the blood during acute renal allograft rejection. This study evaluates the diagnostic utility of a sandwich enzyme immunoassay test for serum and urine IL-2R in renal allograft recipients. A rise in serum IL-2R during the week prior to the clinical diagnosis of rejection correlated better with rejection than did isolated serum IL-2R levels or urine values. For the diagnosis of acute rejection, a rise in serum IL-2R (sensitivity 73%, specificity 87%) was comparable in overall test performance to a rise in serum creatinine (sensitivity 70%, specificity 84%). Overall, the two tests had equivalent receiver operating characteristic curves. Because the etiology of false positives in creatinine and IL-2R assays differed (primarily cyclosporine toxicity and infection, respectively), the predictive value of the combined tests was superior to either alone.

Creatinine↗
PubMed1989

Fc-receptor for mouse IgG1 (Fc gamma RII) and antibody-mediated cell clearance in patients treated with Leu2a antibody.

A pilot study was performed to explore the clinical potential of Leu2a antibody in reversing acute renal allograft rejection. Anti-Leu2a, a murine IgG1 monoclonal antibody (mIgG1 mAb), is specific for the CD8 molecule that is expressed in high density on class I reactive T cells. Of the 6 recipients treated with anti-Leu2a, two responded with a complete reversal of rejection with long-term allograft function maintained for over a year. In two other recipients, acute rejection was initially reversed, but later rejection episodes resulted in allograft failure at 2-3 months posttreatment. Rejection in the two other recipients showed no response to Leu2a mAb treatment. Specific depletion of peripheral blood CD8+ cells occurred in four of the six recipients. Even in this small series, it was evident that cell clearance was neither necessary nor sufficient for reversal of rejection. However, a complete correspondence between cell clearance and the ability of the recipients' mononuclear cells to undergo mitogenic response to the mIgG1 anti-CD3 (Leu4) mAb in vitro was noted. Binding of IgG1 mAb to the Fc-receptor (Fc gamma RII/CD32) expressed on blood monocytes is known to be essential for the T cell mitogenic response to soluble mIgG1 CD3 mAb in vitro. Our data suggest that binding to Fc gamma RII may be an essential step in the process of mIgG1 Leu2a mAb-mediated cell clearance in vivo.

Animals↗
PubMed1989

Dietary marine lipids suppress murine autoimmune disease.

Dietary marine lipids reduce both mortality and the severity of glomerulonephritis in inbred murine strains which develop spontaneous autoimmune disease. The protective effects of marine lipids appear to be accounted for by the major n-3 fatty acids in these preparations, 20:5 and 22:6. The n-3 fatty acids in dietary fish oil are extensively incorporated into several lipid classes in the spleen of autoimmune mice, including phosphatidylinositol, phosphatidylethanolamine, plasmalogens and saturated ether-linked phospholipids as well as diacylphosphoglycerides. The effects of dietary marine lipids on autoimmune disease in experimental models are highly specific. Careful controlled trials will be required to establish the role of dietary marine lipids in the therapy of human autoimmune disease.

Animals↗
PubMed1989

Growth factors in wound healing. Single and synergistic effects on partial thickness porcine skin wounds.

Several growth factors are potential mediators of wound healing, although their actual roles, interactions, and therapeutic use are not established. Six well-characterized human growth factors were chosen for detailed investigation by topical application to standardized skin wounds in swine: epidermal growth factor (EGF), transforming growth factors alpha and beta (TGF-alpha and TGF-beta), fibroblast growth factor (FGF), insulin-like growth factor-I (IGF-I), and platelet-derived growth factor (PDGF). When applied singly in doses up to 1,500 ng, only TGF-beta produced a marked tissue response, as demonstrated by an increase in the new connective tissue volume, the collagen content and maturity, and increased angiogenesis. However, TGF-beta enhanced inflammation and caused abnormal epithelial differentiation and decreased epithelial volume, the last reversed by addition of IGF-I. Recombinant PDGF-2 homodimer, if given in combination with recombinant IGF-I, caused a similar increase in the new connective tissue volume and collagen content and maturity, but without increased inflammation. In addition, this combination stimulated increased amounts of epithelium with normal differentiation. The synergy of PDGF-2 and IGF-I was optimal at a ratio of 2:1 by weight. Of the six individual factors and nine combinations tested, the combinations of PDGF-2 and IGF-I or PDGF-2 and TGF-alpha were the most potent stimulators of healing in the absence of increased inflammation.

Animals↗
PubMed1989

Pathology in the new pathway of medical education at Harvard Medical School.

In 1985 Harvard Medical School initiated an experimental curriculum that incorporated many of the recommendations of the report on the General Professional Education of the Physician (GPEP). Key features are problem-based small group tutorials that emphasize active learning, with increased independent study time and a decreased number of lectures. Tutors serve as guides to their students and are not necessarily experts in the discipline of the cases studied. Learning skills are taught, including information acquisition and criticism and computer literacy. Knowledge is integrated from the beginning by interdisciplinary basic science courses, by earlier introduction of the clinical sciences, and by juxtaposition of the scientific and humanistic aspects of medicine. Preventive medicine, health maintenance, and ambulatory care are given more attention. The students are organized into societies that provide vertical integration and promote cooperation among students and closer contact with faculty. Pathology has proved to be a popular and key bridge in the new curriculum. The success of the early efforts at Harvard and several pioneering medical schools should encourage others to move toward more problem-solving, student-centered, integrative medical education.

Curriculum↗
PubMed1989

Role of fibronectin and fibrinogen in healing of corneal epithelial scrape wounds.

A provisional fibronectin (Fn)-fibrinogen (Fg) matrix forms de novo on the bare basement membrane (BM) surface of superficial epithelial scrape wounds in rabbit and guinea pig (GP) corneas. We determined whether such a substrate is essential for epithelial cell adhesion and migration, using three different approaches. (1) Polyclonal and monoclonal IgG reactive against GP Fn were topically administered to inhibit Fn formation in a GP epithelial scrape wound model. Immunofluorescence studies showed that deposition of both Fn and Fg was inhibited in antibody-treated corneas. During the first 38 hr after wounding, the healing rates were 0.46 +/- 0.06 mm2/hr in control eyes, 0.43 +/- 0.05 mm2/hr in those treated with rabbit polyclonal IgG anti-GP Fn and 0.45 +/- 0.09 mm2/hr in those treated with murine monoclonal IgG anti-GP Fn (P greater than 0.4). (2) In a rabbit epithelial scrape wound model, ancrod was administered intravenously to induce systemic Fg depletion. Fg deposition was completely inhibited on the wound surface, but Fn deposition was not suppressed. The healing rate was 1.24 +/- 0.41 mm2/hr in ancrod-treated corneal wounds and 1.19 +/- 0.29 mm2/hr in control eyes during the first 48 hr after wounding (P greater than 0.5). These data from the antibody and ancrod inhibition indicate that Fg binds to Fn and that Fn binds to components other than Fg.(ABSTRACT TRUNCATED AT 250 WORDS)

Ancrod↗
PubMed1989

Role of fibronectin in the healing of superficial keratectomies in vitro.

A fibronectin (Fn)-fibrinogen (Fg) surface matrix is not essential for epithelial cell migration in a corneal epithelial scrape wound model, in which the basement membrane is preserved. We have therefore tested whether such a provisional scaffolding becomes more critical in a superficial keratectomy model, when the basement membrane is surgically removed. Exogeneous Fn at 0.3 mg/ml was added to the medium of organ cultures of rabbit superficial keratectomies. At 48 hr after wounding, the healing rate was 1.12 +/- 0.03 mm2/hr in control corneas and 1.11 +/- 0.03 mm2/hr in those cultured with Fn. At 64 hr after wounding, the healing rates were also not significantly different (P greater than 0.5). Immunofluorescence studies showed that Fn was not detectable on the surface of control corneas but could be depicted under the migrating epithelium. In corneas cultured with Fn, it diffused throughout the entire stroma but did not deposit as a surface matrix. We therefore attempted to obtain formation of a provisional Fn-Fg surface matrix before establishment of the in vitro organ culture by leaving the superficial keratectomies in vivo for 8 hr, 24 hr or 64 hr. At 64 hr after wounding, their healing rate was 0.80 +/- 0.04 mm2/hr, 0.86 +/- 0.04 mm2/hr and 0.85 +/- 0.06 mm2/hr, respectively, which were not significantly different from that of contralateral ex vivo-wounded cultured corneas (0.83 +/- 0.04 mm2/hr, P greater than 0.5). Immunofluorescence studies revealed a Fn matrix on the bare surface of in vivo-wounded specimen, which was not detectable on ex vivo-wounded cultured corneas; there was also no diffuse stromal Fn.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗