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Biomedical subjects

T Mohanakumar

Publications and source records attributed to T Mohanakumar.

At least 163 records · Page 9Linked to original sources
PubMed1994

Human peripheral blood lymphocyte reconstituted severe combined immunodeficient (hu-PBL-SCID) mice. A model for human islet allograft rejection.

Severe combined immunodeficient (SCID) mice have become a promising tool for the development of models of human immunologic process. We report the development of a reproducible technique for engrafting SCID mice with human PBL (hu-PBL-SCID). Our results show that a booster injection of anti-CD3 antibody stimulated human lymphocytes given 2 days after the initial injection of lymphocytes will improve the efficiency of chimera establishment to 86.7% (13 out of 15). There was also good correlation among detection of human Ig, human CD3+ cells, and human DNA by polymerase chain reaction amplification in the circulation of hu-PBL-SCID mice. Questions remain concerning the immune function of the human lymphoid cells in the SCID mouse. In this study, we analyzed the ability of human T cells in SCID mice to reject human islet allografts transplanted under the kidney capsule. Human islet allograft function assessed by human C-peptide levels demonstrated failure of islet allografts within 21 days after transplantation in hu-PBL-SCID. In contrast, human islets grafted in unreconstituted SCID mice continued to function for greater than 60 days. Recovered human T cells from rejected islets of hu-PBL-SCID mice displayed specific cytolytic activity against HLA class I-matched islets, while the recovered cells from spleen of hu-PBL-SCID mice showed minimal specific cytotoxicity against islets. These results suggest that graft-infiltrating lymphocytes were activated by the engrafted islets within the hu-PBL-SCID, causing the eventual rejection of the human islet allograft. Thus, engraftment of the anti-CD3 antibody-primed human PBL results in a mouse-human chimera with a functionally competent human immune system that is capable of rejecting a human islet allograft.

Animals↗
PubMed1994

Induction immunosuppression with antilymphocyte globulin or OKT3 in cadaver kidney transplantation. Results of a single institution prospective randomized trial.

Improved cadaver kidney allograft survival rates, shorter duration of acute tubular necrosis, and a reduction in the incidence of rejection have been achieved using "quadruple sequential therapy"--AZA, prednisone, and antilymphocyte globulin (ALG) induction followed by the delayed addition of CsA. OKT3 has been shown to be effective in preventing and treating rejection, including steroid- and ALG-resistant rejection episodes. A single institution prospective randomized trial comparing ALG and OKT3 prophylaxis in first cadaver kidney allograft recipients was performed to assess their relative advantages and disadvantages. First cadaver kidney allograft recipients were prospectively randomized to receive 7 days of either ALG (n = 58) or OKT3 (n = 59) as part of a quadruple therapy protocol that included AZA, prednisone, and oral CsA. Patient characteristics, patient survival and causes of death, graft survival and causes of graft loss, incidence of and time to rejection and response to treatment, incidence of infections and their type, renal function, and antibody formation to ALG and OKT3 were examined. The 1-, 2-, and 3-year actuarial patient survival rates were 96% in the ALG group and 98% in the OKT3 group. The graft survival rates were 81.1%, 78.4%, and 78.4% in the ALG group and 84.1%, 78.7%, and 78.7% in the OKT3 group. In ALG-treated patients, 63% never had rejection, compared with 49% in the OKT3 patients (P = NS). In the ALG group 31% had a single rejection, 6% had 2 rejections, and none had 3 rejections, compared with 37%, 12%, and 2% in the OKT3 group. In the ALG group, 43% were steroid responsive compared with 65% in the OKT3 group (P = 0.08). There were 1.44 infections per patient in the ALG group compared with 0.76 in the OKT3 group (P = 0.0004). In the ALG group, 37% of patients developed CMV disease compared with 10% in the OKT3 group (P = 0.001). In donor-positive/recipient-negative patients, 8/10 (80%) in the ALG group developed CMV infection, of which 6 (75%) had severe or moderate CMV disease, compared with 2/15 (13%) patients in the OKT3 group (P = 0.002), of whom only one (6.7%) developed moderate disease. In donor-positive/recipient-positive patients, 8/23 (35%) in the ALG group developed CMV infection, of whom 5/8 (62.5%) developed severe or moderate disease compared with 1/21 (4.8%) in the OKT3 group (P = 0.02). Antibody formation to ALG and OKT3 occurred in 11% and 8% of patients, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1993

Cloning of a unique human homologue of the Escherichia coli DNAJ heat shock protein.

A human homologue of the bacterial DNAJ heatshock protein, HDJ-2, was isolated from a human umbilical vein endothelial cDNA library using a monoclonal antibody which reacts specifically to human endothelial cells and monocytes. This cDNA clone consists of 1469 nucleotides with an open reading frame of 1191 nucleotides. HDJ-2 shares significant homology with Escherichia coli heat shock protein DNAJ, as well as the yeast homologues Sec63, YDJ1, SCJ1 and SIS1. This homology suggests HDJ-2 may be involved in protein folding and/or transport.

Amino Acid Sequence↗
PubMed1993

CD32C (Fc gamma RIIC) mRNA expression and regulation.

The cell surface expression of the CD32 receptors for the Fc portion of immunoglobulin G (Fc gamma RII-CD32) is regulated by agents such as phorbol esters (PMA) and cytokines. In this study, we investigated the effects of PMA and interferon-gamma (IFN-gamma) on the expression of CD32C mRNA in U937 cells. When U937 (CD32+) cells are incubated with either PMA or IFN-gamma a significant enhancement of CD32C mRNA expression is observed with maximum enhancement at 18 hrs post-PMA and IFN-gamma addition. The addition of actinomycin D (ActD), a transcriptional inhibitor, together with either PMA or IFN-gamma diminishes the enhanced levels of CD32C mRNA to the basal levels, indicating that transcriptional regulation is involved in this modulatory process. The addition of cyclohexamide (CX), a protein synthesis inhibitor, to cultures undergoing stimulation with either PMA or IFN-gamma, increased the levels of CD32C mRNA synthesis suggesting that regulatory degradation proteins may be involved. The PMA and IFN-gamma stimulated CD32C mRNA is degraded within 2 hr post-stimulation and this degradation is delayed by the inhibition of de novo protein synthesis. These results, taken together with our previous studies of CD32A mRNA regulation in U937 cells stimulated with PMA, indicate that both the CD32A and C isomer mRNAs are rapidly degraded; however, CD32A and C isomer mRNAs are differentially regulated. At the optimal PMA dose, the time of mRNA stimulation of CD32A and C mRNA varies and the addition of CX to U937 cells together with PMA enhanced the levels of CD32C mRNA but had no effect on CD32A mRNA levels. These results imply that the differential regulation of the two CD32 isomers may result in differential function.

Antigens, CD↗
PubMed1993

Kidney cell-restricted recognition of MHC class I alloantigens by human cytolytic T cell clones.

The kidney expresses antigens not generally expressed by other cells in the body. To test the hypothesis that kidney-restricted antigens alter T cell recognition of MHC class I alloantigens, a panel of human T cell clones was established using an allogeneic kidney cell line (KCL) as the source of stimulator cells. Unexpectedly, a majority of these clones lysed the stimulating KCL in an allospecific manner but completely failed to lyse lymphoid cell targets derived from the KCL donor. Three of the KCL-reactive clones have been characterized in detail. All three are CD8+/CD4-, alpha/beta TCR,+ and their lytic activity is blocked by monoclonals to HLA class I framework determinants. Mapping studies using a panel of KCL targets, and blocking studies with allele-specific monoclonals indicated that clone 1-5 is directed to HLA-A3, clone 3-10 to HLA-B62 (putatively), and clone 5-2 to HLA-B51. Direct lysis and cold target inhibition assays demonstrated that clones 1-5 and 3-10 recognize their target class I alloantigens on KCL but not on EBV-transformed B cells or PHA-stimulated T cells. FACS analysis and HLA phenotyping excluded quantitative or qualitative deficiencies in HLA class I expression on the lymphoid cell targets as likely mechanisms of tissue specificity. These data suggest that kidney-restricted antigens may play a role in T cell recognition of MHC class I alloantigens, and they raise the possibility that parenchymal cell-restricted effector populations may contribute to rejection of renal allografts.

Cell Line↗
PubMed1993

Probable antibody-mediated failure of two sequential ABO-compatible hepatic allografts in a single recipient.

Two sequential ABO-compatible orthotopic liver allografts failed, despite excellent initial posttransplant function, in a patient with preformed donor-specific alloantibodies. There was no evidence of cell-mediated rejection. Retrospective crossmatching of recipient serum, obtained immediately prior to the first transplant, revealed the presence of lymphocytotoxic antibodies directed against donor class I HLA B17, at a titer of greater than 1:32,768. Similarly, lymphocytotoxic antibodies directed against the second donor's class I HLA A2 phenotype were detected on retrospective crossmatching utilizing both the three-wash Amos technique (TWA-CDC), and the anti-human immunoglobulin augmented technique (AHG-CDC), at a titer of greater than 1:32,768. Anti-class I specific alloantibodies were eluted from both failed liver grafts at titers of 1:256. The hepatic necrosis in zones 3 and 2 that were observed on histologic examination, and the profound refractory consumptive thrombocytopenia subsequent to each transplant may have been the result of antibody-mediated rejection by preformed lymphocytotoxic antibodies. Despite the liver's remarkable capacity to withstand antibody-mediated injury, primary humoral rejection following ABO compatible liver transplantation may occur if extremely high titers of performed allospecific lymphocytotoxic antibodies are present.

ABO Blood-Group System↗
PubMed1993

Induction of donor-specific tolerance to cardiac but not skin or renal allografts by intrathymic injection of splenocyte alloantigen.

We have recently found that donor-specific tolerance to a cardiac allograft can be achieved after the intrathymic (i.t.) injection of donor splenocytes and a single intraperitoneal injection of rabbit antirat lymphocyte serum. The present study evaluated whether the tolerance induced by splenocytes injected i.t. could also prevent the rejection of kidney and skin allografts. Male Buffalo (RT1b) rats were given 25 x 10(6) fully MHC-mismatched unfractionated Lewis (RT1l) splenocytes by i.t. injection plus 1 ml of ALS i.p. and 21 days later underwent a Lewis heterotopic cardiac, orthotopic renal, or skin transplant. Lewis i.t. injection induced a donor-specific tolerance with indefinite cardiac allograft survival (> 153.1 days) in 88% of the recipients without the need for further immunosuppression, while renal and skin allograft survival was prolonged (kidney 14.8 days vs. control 7.8 days; skin 11.6 days vs. control 9.2 days) but were still rejected. Buffalo recipients with a long-surviving Lewis cardiac allograft after Lewis i.t. injection were still able to reject a third-party heterotopic ACI (RT1a) cardiac allograft in normal time (7.0 days), but did not reject a second Lewis cardiac allograft (> 100.0 days). In contrast, however, Buffalo recipients with long-surviving Lewis cardiac allografts did reject a Lewis skin allograft in normal time (10.0 days) and a Lewis renal allograft in a prolonged manner (17.6 days) without causing the rejection of the Lewis cardiac allografts. These data support the important role tissue-specific non-MHC antigens may play in the rejection of kidney and skin allografts.

Animals↗
PubMed1993

Development of autoantibodies to T cell clonotypic structures in a liver-kidney allograft recipient.

To elucidate the mechanism of human liver allograft rejection and acceptance, T cell clones were established from liver biopsies of a liver-kidney transplant recipient during a rejection episode. Five of the clones were characterized and found to be CD4+, alpha/beta positive T cells that proliferated specifically to the mismatched donor HLAs. Using an immunofluorescence assay, it was observed that three of these clones were recognized by autologous antibodies developed during the post-transplant period between 18 months and the end of the testing period of 36 months. Furthermore, by capping experiments, it was determined that these antibodies were recognizing the CD3-TCR complex. This was confirmed by immunoprecipitation and sequential immunoprecipitation followed by SDS-PAGE and autoradiography of lysates of radiolabeled T cell clones. Thus, our data indicate that donor-reactive T cells infiltrate into the liver allograft during rejection episodes, and that autologous antibodies reactive to the CD3-TCR complex of these cells are developed in the post-transplant period. These results support the hypothesis that the development of auto-antibodies directed against or cross-reactive to the clonotypic structures of the donor-reactive lymphocytes may play an important role in the down-regulation of the immune response against the allograft.

Autoantibodies↗
PubMed1993

Characterization of antiidiotypic antibodies to donor HLA that develop after liver transplantation.

Several studies have reported the development of antiidiotypic antibodies to anti-HLA alloantibodies in renal allograft transplant recipients, postulating their potential beneficial role in allograft survival. In order to evaluate the role of anti-HLA antiidiotypic antibodies in human liver transplant recipients and to differentiate them from circulating soluble donor HLA antigens, sera obtained from liver recipients, both pre- and posttransplantation, were analyzed for cytotoxicity inhibitory activity against alloantisera to mismatched donor HLA antigens. Prior to cytotoxicity inhibition assays, sera were absorbed with W6/32 coupled sepharose in order to remove circulating HLA antigens. Antiidiotypic antibodies to anti-HLA class I antibodies were detected in the sera of 7 out of 9 recipients, and antibodies to anti-HLA class II were found in the sera of 4 out of 7 recipients. Antiidiotypic antibodies were detected only during the immediate posttransplantation period. The specific inhibitory activity noted against both HLA class I and II mismatches showed no detectable preference for either HLA class or locus. Furthermore, the antiidiotypic antibodies to HLA developed in liver recipients also inhibited alloantisera to HLA-specific public epitopes or crossreactive groups (CREGS). Cytotoxicity inhibition by posttransplant sera was not mediated by circulating HLA antigens since absorption of the sera with monoclonal anti-HLA framework reagents did not change the specific inhibition of the alloantisera. In addition, the immunoglobulin fraction of the posttransplant sera retained its ability to inhibit cytotoxicity by donor-specific alloantisera. Thus these studies indicate that the development of antiidiotypic antibodies to anti-HLA is common during the immediate period following liver transplantation, even though circulating donor HLA antigens are present. The presence of circulating donor HLA antigens and the development of antiidiotypic antibodies to donor-specific anti-HLA during this period may be important for the successful adaptation of mismatched liver allografts.

Antibodies, Anti-Idiotypic↗
PubMed1993

Analysis of T cell responses in liver allograft recipients. Evidence for deletion of donor-specific cytotoxic T cells in the peripheral circulation.

Analysis of cell-mediated lympholysis in long-term liver allograft recipients indicated that there was a donor-specific unresponsiveness that could not be reversed by the addition of rIL-2 and/or mixed lymphocyte culture supernatant or by nonspecific stimulation of the cultures with PHA. Stimulation of recipient cells with semisyngeneic cells having both donor and third-party HLA antigens failed to reveal the presence of cytotoxic T cells (CTL) specific to the donor, whereas the CTL response to third-party antigens remained normal. Removal of B lymphocytes from the responding cell population did not influence the responses. Furthermore, limiting dilution analysis showed that the liver transplant recipients did not have detectable levels of CTL precursors (CTLp) reactive to the donor antigens, whereas their CTLp to third-party antigens remained normal. Donor-specific CTLp were present before and during the early post-transplant period; these cells were eliminated from the peripheral circulation by 10 mo after transplantation. Taken together, these results indicate that there is a deletion of CTLp specific to donor MHC antigens in the peripheral circulation of long-term liver allograft recipients that may account in part for the success of liver transplantation across MHC barriers.

Adult↗
PubMed1992

Evidence for cross-regulation of Fc gamma RIIIB (CD16) receptor-mediated signaling by Fc gamma RII (CD32) expressed on polymorphonuclear neutrophils.

Human polymorphonuclear neutrophils (PMN) express the low affinity receptors for the Fc domain of IgG (Fc gamma R), Fc gamma RII (CD32), and the glycosyl phosphatidylinositol-linked isoform of Fc gamma RIII (Fc gamma RIIIB, CD16) on their cell surface. Both of these receptors have been shown to be signal-transducing molecules. However, the mechanisms involved in such signaling are not clearly understood. In this report, we investigated intracellular Ca2+ ([Ca2+]i) signals triggered in PMN by both the receptors using aggregated human IgG (AggIgG) and specific mAb to Fc gamma RII (KuFc79) and Fc gamma RIII (3G8) as ligands. Addition of AggIgG as well as cross-linking of mAb KuFc79 and 3G8 bound to PMN induced [Ca2+]i flux. However, preincubation of PMN with mAb KuFc79 (whole Ig or Fab fragments) in the absence of cross-linking abrogated the [Ca2+]i flux induced by AggIgG and mAb 3G8, indicating that Fc gamma RII receptor occupancy by mAb KuFc79 can block signals mediated by Fc gamma RIIIB. KuFc79-isotype-matched control mAb (MOPC 195) did not abolish the signals generated by AggIgG and mAb 3G8. In addition, mAb KuFc79 did not abrogate [Ca2+]i responses elicited by the receptor for the chemotactic peptide FMLP indicating that modulation of signal transduction by Fc gamma RII-bound KuFc79 is selective for certain receptors. Immunofluorescence analysis of PMN initially treated with mAb KuFc79 followed by AggIgG showed that KuFc79 did not block the binding of AggIgG to PMN. Similarly, competitive binding studies revealed no stearic hindrance between mAb KuFc79 bound to Fc gamma RII and mAb 3G8 bound to Fc gamma RIIIB. Thus, the ability of mAb KuFc79 to modulate signals induced by AggIgG and 3G8 strongly suggests that Fc gamma RII may regulate Fc gamma RIIIB signaling. While previous studies on Fc gamma RII revealed a requirement for cross-linking of the receptor to induce its effector functions, the present study shows that binding of mAb KuFc79 to Fc gamma RII itself, even in a univalent form, results in cross-regulation of Fc gamma RIIIB-triggered signals. Treatment of PMN with protein tyrosine kinase inhibitors, genistein and herbimycin A, abrogated the [Ca2+]i signals elicited by both mAb KuFc79 and 3G8. These results suggest that tyrosine kinase enzyme(s) associated with these receptors may be crucial for positive/negative signals triggered by Fc gamma RII and Fc gamma RIIIB.

Antibodies, Monoclonal↗
PubMed1992

CD32A (Fc gamma RIIa) mRNA expression and regulation in blood monocytes and cell lines.

The cell surface expression of the CD32 receptors for the Fc portion of immunoglobulin G (Fc gamma RII) is highly regulated by agents such as phorbol ester (PMA) and cytokines. In this study we investigated the regulatory effects of PMA, aggregated IgG (AIgG) and KuFc79 anti-CD32 monoclonal antibodies (mAb) on the expression of the CD32A isomer mRNA. When U937 (CD32+ cells) are incubated with PMA a significant enhancement of the CD32A isomer mRNA is observed. The CD32A mRNA is also markedly enhanced when the CD32+ K562 cells are incubated with AIgG and anti-CD32 mAb but not with control MOPC-195 mAb. The addition of actinomycin D (ActD), a transcriptional inhibitor together with PMA, AIgG or KuFc79 mAb diminishes the enhanced levels of CD32A mRNA to the basal, constitutively expressed levels, implicating transcriptional regulation in this modulatory process. The PMA induced mRNA is rapidly degraded while the constitutively expressed CD32A mRNA is not, suggesting differential regulation of the stimulated vs the unstimulated CD32A mRNA. Inhibition of protein synthesis does not significantly affect the upregulation of CD32 mRNA by PMA, AIgG or KuFc79 in U937 and K562 cells. The upregulation of CD32A mRNA observed in the cell lines U937 and K562 is also detected when normal blood monocytes are used. Similarly to the cell lines the enhancement of CD32A mRNA in monocytes is blocked by ActD.

Adolescent↗