Biomedical subjects

T Mohanakumar

Publications and source records attributed to T Mohanakumar.

At least 145 records · Page 8Linked to original sources

PubMed1997

Increased concentration of soluble human leukocyte antigen class I levels in the bronchoalveolar lavage of human pulmonary allografts.

BACKGROUND: Human leukocyte antigen (HLA) class I antigens, are glycoproteins expressed on the cell surface and are also secreted (sHLA) into the surrounding fluids. This study investigates whether pulmonary allograft rejection is associated with an increased amount of sHLA class I in the bronchoalveolar lavage (BAL) fluid. METHODS: Enzyme-linked immunosorbant assays were used to measure sHLA class I levels in BAL samples from 66 lung transplant recipients. RESULTS: Analysis of pulmonary allograft recipients revealed that the mean concentration of sHLA class I was significantly higher in samples from recipients with acute rejection than in recipients with no evidence of rejection. Seventy-two percent of the patients with rejection had sHLA levels above the normal range for patients with infection or rejection. Conversely, sHLA levels were within normal limits in 94% of the control population. Time kinetic analysis revealed that in subjects with rejection, sHLA class I levels peaked in the first 2 weeks after transplantation and decreased thereafter. Increased levels of sHLA were found in patients with acute rejection but not in those with chronic rejection. Fifty-nine percent (n = 10) of the patients with infection had sHLA levels within the normal (no infection or rejection) range. The remaining 41% (n = 7) with infection had sHLA above the normal range. Fifty-seven percent (n = 4) of the latter group had cytomegalovirus infection. These results were confirmed in a prospective study carried out by analyzing paired samples obtained during and after rejection. Eight of the nine patients had high BAL sHLA class I during acute rejection, and low BAL sHLA class I levels after resolution of the acute rejection. CONCLUSION: Our data demonstrate that measurement of sHLA class I levels in BAL samples is a sensitive indicator of acute rejection.

Acute Disease↗

PubMed1996

Biochemical and immunological evaluation of donor-specific soluble HLA in the circulation of liver transplant recipients.

MHC antigens, normally expressed as integral membrane proteins, are also present in soluble form in the peripheral circulation. These soluble human leukocyte antigens (sHLA) are found at elevated levels in patients with a variety of infections as well as in organ transplant recipients. In liver transplant recipients, however, most of the circulating sHLA are of donor phenotype, especially during the early posttransplant period. Here we report the purification and characterization of sHLA of both recipient and donor origin from liver transplant recipients. It was observed that sHLA consisted of four major polypeptides having molecular mass of 44, 41, 35-37, and 12 kD complexed with IgM and IgG antibodies. Further analysis revealed that these immunoglobulins contained anti-HLA antibodies. Analysis of the affinity-purified materials by a number of approaches failed to detect any other fragment(s) of HLA class I heavy chain polypeptides smaller than 12 kD. No significant difference was observed in the biochemical nature of the sHLA of donor and recipient origin and they were similar to those found in normal individuals. Affinity-purified HLA-A3 inhibited the cytolytic activity of an HLA-A3-specific CD8+ T cell line, whereas, purified sHLA-A2 failed to inhibit anti-HLA-A3 CTL activity. Further, the proliferation of the T cell line was not inhibited by sHLA-A3. Thus, the inhibitory activity shown by sHLA was antigen-specific and directed against a functional subset of T lymphocytes. These results support the notion that sHLA may play an important regulatory role in the immune response to allograft in humans.

Adult↗

PubMed1996

Increased expression of the HDJ-2 heat shock protein in biopsies of human rejected kidney.

The presence of donor-specific alloreactive helper and cytotoxic T cells has been described in allograft biopsies obtained from individuals undergoing acute allograft rejection of various solid organs. However, not all of these lymphocytes demonstrated specificity to mismatched donor HLA antigens. The identity of the antigens to which these T cells are directed to is still unknown at present. The possibility that heat shock proteins (Hsp) could serve as antigenic determinants to which these T cells respond has been raised. We have recently cloned and characterized a novel Hsp of 45Kd molecular weight. In the present study we show that the synthesis of this Hsp (HDJ-2) as well as Hsp60 is significantly elevated in kidney biopsies from individuals undergoing acute and chronic rejection. No message was detected either for HDJ-2 or Hsp60 in biopsies obtained from normal pretransplant kidneys or posttransplant kidneys with no rejection. However, there was some increase in Hsp in miscellaneous causes of allograft dysfunction such as infection and drug allergy. But, this was not as consistent as that noted for allograft rejection. This marked increase in Hsp expression during allograft rejection suggests Hsps as potential candidates for antigenic determinants contributing to kidney rejection.

Acute Disease↗

PubMed1996

Biochemical and functional characterization of xenoreactive natural antibodies in hu-PBL-SCID mice.

An in vivo model system to understand the mechanism of xenograft rejection was established using human peripheral blood leukocyte-reconstituted SCID (hu-PBL-SCID) mice. Human xenoreactive natural antibodies (XNA), of IgM and IgG subtypes, capable of binding to pig aortic endothelial cells (PAEC) were detected in the sera of hu-PBL-SCID by ELISA and flowcytometric methods. Western blot analysis of PAEC lysates showed that IgM and IgG XNA from hu-PBL-SCID recognized xenoantigens with similar molecular mass as those recognized by XNA from normal human serum (NHS). This result demonstrated that hu-PBL-SCID contained XNA representing the same repertoire as that of the NHS. XNA from NHS and hu-PBL-SCID were also able to induce intracellular Ca2+ signals in cultured PAEC several fold above the basal level. This result revealed their functional similarity and demonstrated for the first time that XNA in the absence of C can activate PAEC, which may lead to the pathology of xenograft rejection. In vivo, PAEC transplanted under the kidney capsule of hu-PBL-SCID mice showed deposition of human IgM and mouse C. In summary, the present study demonstrates that hu-PBL-SCID can serve as a useful model to characterize innate immunity against xenograft.

Animals↗

PubMed1996

Evidence that pediatric liver transplant recipients may undergo late rejection episodes in spite of donor-specific microchimerism.

Lymphocytes of donor origin can be demonstrated in the blood of many liver transplant recipients. It has been proposed that this chimerism may imply graft tolerance and permit withdrawal of immunosuppression. We report two children with liver transplants who had lymphocyte chimerism demonstrated at the time of late rejection episodes. One child was chimeric for both of his donors, although he retained the first allograft for only 3 days. Thus, the persistence of donor lymphocytes may be unrelated to the presence of the donor organ. Graft rejection can occur in spite of donor-specific microchimerism. The role of donor-specific microchimerism in graft acceptance or graft tolerance remains to be elucidated.

Base Sequence↗

PubMed1996

Gadolinium chloride inhibits Kupffer cell nitric oxide synthase (iNOS) induction.

Kupffer cells (KC) are the phagocytic macrophages of the liver. The rare earth metal, gadolinium (GdCl3), is a lanthanide, which, after phagocytosis by the KC, has been found to alter various aspects of KC physiology. In this study, we describe for the first time that the in vivo administration of GdCl3 to rats decreases the release of NO by isolated rat KC in response to lipopolysaccharide. Western blot analysis shows decreased expression of both inducible nitric oxide synthase as well as total cellular calmodulin after GdCl3 treatment. Possible mechanisms for this phenomenon are suggested.

Animals↗

PubMed1996

Cytolytic effector mechanisms of human CD4+ cytotoxic T lymphocytes.

To elucidate mechanisms by which human CD4+ cells mediated cytolytic activity, we studied the expression of cytolytic proteins and the effects of inhibitors and mAbs on T-cell clones. Of seven cytolytic CD4+ clones, three were specific for the HLA-DR17, while four recognized DR18. Anti-HLA-DR mAb and anti-CD4 mAb blocked lysis. In addition, N alpha-p-tosyl-L-lysine chloromethylketone (TLCK), a serine esterase inhibitor, as well as cytochalasin B and monensin, antagonists of secretory pathways, inhibited CD4+ CTLs, whereas the absence of extracellular Ca+2 or the presence of Ca+2 channel blockers partially inhibited cytotoxicity. CD4+ CTLs induced apoptosis of target cell nuclei and membrane damage simultaneously. The CD4+ clones synthesized perforin and granzyme B and expressed the granule-associated protein TIA-1. Our studies indicate that two distinct mechanisms may contribute to cytolysis by CD4+ clones: (1) a Ca+2-dependent mechanism associated with the cytotoxic granules and (2) a Ca+2-insensitive mechanism.

Base Sequence↗

PubMed1996

Indirect allorecognition of HLA class I peptides by CD4+ cytolytic T lymphocytes.

T-cell responses to alloantigens can occur either by "direct" recognition of donor MHC molecules, or "indirect" recognition of MHC peptides in association with self-MHC. To evaluate human T cells mediating indirect allorecognition, a CD4+ TCL and clones specific for HLA-A1 or HLA-B8 (residues 60-84) were generated from normal PBLs (A2,29 B62,- DR1,4 DQ3). Most clones were A1 specific (16 out of 17 tested), HLA-DR4 restricted (8 out of 8), and lysed targets pulsed with A1 peptide (16 out of 16). An amino acid substitution at position 86 of the DR4 beta chain (G -> V) abrogated the capacity of CD4+ CTLs to lyse target cells. Chloroquine treatment of A1-pulsed targets reduced their susceptibility to lysis, indicating a requirement for peptide processing. The TCL and clones were stimulated to proliferate by cells bearing intact HLA-A1 when autologous APCs were present, indicating that the epitope contained within the A1 60-84 peptide being recognized is produced when APCs process native HLA-A1. Furthermore, the clones and TCL did not recognize HLA-A1 on target cells carrying this allele plus self-HLA-DR4. These studies suggest a much wider role for CD4+ T cells in allograft immunity.

Antigen Presentation↗

PubMed1996

Human peripheral blood lymphocyte-reconstituted, severe combined immunodeficient mice as a model for porcine islet xenograft rejection in humans.

Previously we established human peripheral blood lymphocyte-reconstituted severe combined immunodeficiency (SCID) (hu-PBL-SCID) mice as a model for human islet allograft rejection. The function of xenografted hu-PBL was confirmed to reject human alloislets in hu-PBL-SCID mice. In this study, we modified this model as a porcine islet xenograft to study porcine islet rejection in humans. Chimeric mice were used as the recipients of porcine islets to reveal the mechanisms of xenograft rejection in humans. SCID mice were reconstituted with 30 x 10(6) of hu-PBL initially, and 10 x 10(6) of antihuman CD3-primed PBL was injected intraperitoneally 2 days later as a booster. An additional booster injection provided greater possibility (86.7%, n = 15) of chimera establishment as well as a higher human immunoglobulin concentration in SCID mice than the single injection group. In an in vitro assay, sera from hu-PBL-SCID mice were found to recognize porcine islets by FACS staining. In an in vivo study, immunofluorescent analysis of a frozen section showed that human immunoglobulins adhered to the xenografted porcine islet under the kidney capsule of hu-PBL-SCID mice. Although no mouse immunoglobulins were detected on sections, mouse complement (C3) was shown to adhere to the xenografted porcine islet. Thus, hu-PBL-SCID mice provide a useful model for investigating the real-life situation of porcine islet xenograft rejection in humans.

Animals↗

PubMed1995

Donor-specific transfusions have long-term beneficial effects for human renal allografts.

From April, 1980 to November, 1988, 163 one or two haplotype-mismatch living related (LR) or living unrelated (LUR) potential renal transplant recipients received three 200 ml aliquots of donor specific transfusion (DST) at biweekly intervals with concomitant azathioprine (2 mg/kg/day). Following transplantation, only prednisone and azathioprine were given for immunosuppression. The results for the DST group are compared with those for HLA identical living recipients (57 patients) transplanted during this same interval (1980-1988). Comparison is also made with a group of one or two haplotype-mismatched living donor recipients (54 patients) not treated with DST but with triple drug therapy (prednisone, azathioprine, cyclosporine) and antithymocyte globulin (ATG) or OKT-3 induction. Permanent T cell crossmatch sensitization occurred in 11 of 163 patients (7%). Successful DST donor transplants were performed between 121 one HLA haplotype-mismatched, 14 two HLA haplotype-mismatched LR, and 7 two haplotype-mismatched LUR pairs. Actual one- and five-year graft survivals were 94%, 100%, 100%, and 72%, 85%, and 71%, respectively, for these three subgroups of DST treated patients. The graft survival for all DST pretreated recipients at one, five, and ten years was comparable to the HLA-identical group (94%, 79%, 64% vs. 91%, 80% and 77%). At a mean follow-up of 10 1/2 years, 54% (80 patients) of the entire group of 147 patients transplanted after DST have functioning transplants with a mean serum creatinine of 1.7 mg/dl. Fifteen percent of DST patients (21 patients) died with a functioning graft 2 to 132 months after transplantation, 26% (37 patients) rejected the DST graft after 1 to 128 months, and 6% (9 patients) were lost for nonimmunological reasons. No lymphoproliferative disease developed in the DST group and the incidence of cytomegalovirus sepsis was only 2% (3 patients). The long-term beneficial effects of DST on renal allograft survival and function and the lower incidence of the complications of nonspecific immunosuppression should encourage increased utilization of DST in renal transplantation.

Azathioprine↗

PubMed1995

Isolation of a kidney-specific peptide recognized by alloreactive HLA-A3-restricted human CTL.

The molecular nature of tissue-specific Ags involved in MHC-restricted CTL responses is as yet undefined. To determine the specificity of these peptides, their function, and their possible relationship to allograft rejection, we have utilized human kidney-specific CD8+ CTL clones to screen reversed-phase HPLC (RP-HPLC)-separated self peptides presented by allo-class I molecules. One of these clones is HLA-A3-restricted and the other HLA-B62-restricted, lysing human kidney cell lines but not MHC identical B lymphoblastoid cells which express the appropriate HLA molecules. We have identified a biologically active RP-HPLC fraction containing self peptides eluted from affinity-purified MHC molecules from HLA-A3+ kidney. This peptide is not expressed in HLA-A3+ spleen. Similarly, a HLA-B62-associated peptide fraction was identified in kidney but not in spleen using the HLA-B62-restricted CTL clone. Sequence analysis of the biologically active fraction from HLA-A3 kidney revealed multiple peptides. Because of the ambiguity of the peptide sequence, a mixed peptide library corresponding to this sequence was synthesized that included the HLA-A3 binding motif. The biologically active peptide library was RP-HPLC fractionated and the fraction containing HLA-A3-restricted CTL activity was sequenced. The resulting sequence of the alloreactive HLA-A3-restricted peptide epitope is GPPGVTIVK. By using this unique strategy, we describe the successful isolation and sequencing of an antigenic peptide that is recognized by a human alloreactive kidney-specific CTL clone.

Amino Acid Sequence↗

PubMed1995

Immunosuppressive effect of monoclonal antibodies to ICAM-1 and LFA-1 on peripheral nerve allograft in mice.

This study evaluated the immunosuppressive effect of monoclonal antibodies against cell surface molecules in a murine peripheral nerve allograft model. After nerve allografting, 18 recipients were treated with both anti-intercellular adhesion molecule-1 (ICAM-1) and anti-lymphocyte function-associated molecule-1 (LFA-1) monoclonal antibodies in low or high dose. Nerve allografts were harvested at 8 weeks for histologic and morphometric evaluation. Recipients were subsequently challenged with skin grafts at 9 weeks and a cytotoxic assay at 12 weeks. The majority of the antibody-treated allografts (13 of 18) showed excellent regeneration comparable to the autografts with preservation of the normal nerve architecture and scant cellular infiltrate. All untreated allografts demonstrated severe structural disorganization with cellular infiltrate consistent with acute rejection. In the high dose group, the mean skin graft survival time from nerve donor mice, but not third-party mice, was significantly prolonged. (17.5 vs. 11.3 days). Similarly, the cytotoxic activity against nerve donor alloantigen was significantly suppressed. These preliminary findings suggest that antibody therapy alone can facilitate nerve regeneration in a murine nerve allograft model.

Animals↗

PubMed1995

Monoclonal antibodies against ICAM-1 and LFA-1 prolong nerve allograft survival.

In a rat nerve allograft model, specific immunosuppression was approached with monoclonal antibodies (MAbs) against cell-surface molecules. After engraftment, recipients were treated with antiintercellular adhesion molecule-1 (ICAM-1) and antilymphocyte function-associated antigen-1 (LFA-1) MAbs for 14 days. Functional recovery was evaluated biweekly. Electrophysiological and histological assessments were performed at 6 and 16 weeks. Immunologic responsiveness in the recipients was assessed with a cytotoxic T lymphocyte (CTL) assay at 16 weeks and skin grafts at 18 weeks. The untreated allograft group demonstrated complete disruption of fascicular architecture with poor nerve regeneration. The MAb-treated allografts maintained well-organized nerve architecture with a dense population of well-myelinated fibers. These animals showed functional and electrophysiological recovery. Suppression of CTL activity was nerve donor specific and the survival time of nerve donor skin grafts was prolonged, suggesting induction of alloantigen-specific tolerance. MAbs therapy directed against ICAM-1/LFA-1 presents a new approach for the management of the peripheral nerve allograft response.

Animals↗

PubMed1995

Prevalence and outcome of bronchiolitis obliterans syndrome after lung transplantation. Washington University Lung Transplant Group.

BACKGROUND: Bronchiolitis obliterans syndrome (BOS) is the main cause of late morbidity and mortality in lung transplantation. This study was designed to accurately determine the prevalence of this syndrome of chronic lung allograft dysfunction (which is presumed to be due to chronic rejection). METHODS: A retrospective analysis was done of 212 consecutive lung transplantations performed at Barnes Hospital between July 1988 and March 1994 to characterize the prevalence and course of BOS. One hundred eighty-seven transplant recipients survived at least 3 months after transplantation, putting them at risk for BOS. Recipients free of BOS (group I) were distinguished from those with BOS (group II) based on the presence of declining spirometry (forced expiratory volume in 1 second persistently less than 80% of previous baseline) or histologic obliterative bronchiolitis in group II. RESULTS: There were 110 transplantations in group I (59%) and 77 in group II (41%). At follow-up, BOS was detected using the following criteria: declining forced expiratory volume in 1 second alone, 40 of 77 (52%); positive histologic results alone, 7 of 77 (9.1%); and both, 30 of 77 (38.9%). Declining spirometry was the most common initial sign of BOS onset (57 of 77, 74%). There were no differences between groups with respect to age, sex, indication for transplantation, or type of transplantation performed. The mortality rate was significantly higher with BOS (group II, 22 of 77 [28.6%] versus group I, 8 of 110 [7.3%]; p = 0.001) and was not related to either the type of transplantation performed or the indication for transplantation. Follow-up of group II (mean 35.1 months; range, 7.1 to 63.7 months) showed a delay until BOS onset (16.1 +/- 1.2 months); when BOS was fatal, death ensued within 11.5 +/- 2.4 months of its onset. Comparison of the first and last quartiles of recipients in this series (QTR1 versus QTR4, 53 patients in each) demonstrated a higher prevalence of BOS in QTR1 (24 with BOS of 43 at risk [55.8%] versus QTR4, 5 with BOS of 52 at risk [9.6%]; p < 0.001) and a worse BOS functional score in QTR1 (2.2 +/- 0.2 versus QTR4, 0.8 +/- 0.2; p = 0.007). CONCLUSIONS: (1) Bronchiolitis obliterans syndrome is truly a clinical syndrome, not simply a pathologic entity; (2) BOS displays considerable latency in onset and progression; (3) lung transplant recipients must therefore be followed up for a sufficient interval to determine the actual prevalence and mortality rate of BOS; and (4) the prevalence and mortality rates of BOS are higher than previously appreciated, exceeding 50% and 40%, respectively.

Adult↗

PubMed1995

Cytolytic T lymphocytes from human renal allograft biopsies are tissue specific.

The cytolytic activity of T lymphocytes infiltrating renal allografts from recipients undergoing episodes of acute cellular rejection was studied. These T-cell populations, composed of both CD4+ and CD8+ cells, demonstrated significant cytolytic activity against both donor-derived KCLs and B-LCLs. In five of 21 biopsy-derived lines greater cytolytic activity was measured against donor KCLs compared to donor B-LCLs, suggesting the presence of kidney antigen-specific, MHC-restricted clones. Clones developed by stimulation with donor B-LCLs lysed both donor B-LCLs and KCLs while clones developed on donor KCLs as stimulator cells showed tissue specificity. Three of 26 clones recognized tissue-specific antigens in the context of donor MHC class I antigens lysing donor KCLs but not B-LCLs. These data demonstrate that a subpopulation of T cells recognizing kidney-specific antigens are present in biopsies of renal allograft recipients undergoing acute cellular rejection. This subpopulation of tissue-specific cytotoxic T lymphocytes may prove to contribute significantly to the pathology of allograft rejection.

Biopsy↗

PubMed1995

Donor-specific transfusion and donor bone marrow infusion in renal transplantation tolerance: a review of efficacy and mechanisms.

The ultimate goal in transplantation is modulation of the immune response to produce tolerance without immunosuppression. To date only a state of pseudotolerance for the allograft has been achieved through the use of potent pharmacologic and biologic manipulations. Despite these manipulations to prevent acute rejection, chronic rejection eventually results in graft failure. Thus, different strategies have been sought to induce tolerance and prevent acute and chronic rejection. Historically, donor-specific transfusion (DST) was one such strategy attempted. Donor-specific transfusion has been used primarily in living donor organ transplantation. With the concern that DST may sensitize patients, thereby preventing transplantation and introduction of cyclosporine, the use of DST was curtailed. More recently, donor bone marrow (DBM) infusion at the time of cadaveric transplantation has been used to facilitate development of microchimerism and tolerance to abrogate acute and chronic rejection. However, DBM infusion may predispose the recipient to graft-versus-host disease and is not easily accomplished in living donor organ transplantation. The potentially immunomodulating and tolerizing mechanisms of DST and DBM infusion are similar and include induction of anergy, stimulation of anti-anti-HLA antibodies, provision of soluble HLA antigen, suppressor cell and/or veto cell activity, clonal deletion, regulation of cell surface molecules, regulation of cytokines, promotion of microchimerism, or a combination of these. Of these mechanisms, microchimerism with the concomitant persistence of soluble donor HLA antigen is felt by many to be the most important. Although microchimerism is detectable in many patients who are tolerant of their grafts, there is no clear evidence that chimerism is responsible for the induction or maintenance of tolerance.

Animals↗

PubMed1995

Functional analysis of complement receptor 1 using a new monoclonal antibody, KuN241.

A monoclonal antibody (MAb), KuN241, recognized an antigen present on all monocytes, polymorphonuclear leukocytes (PMNs), B cells, and a subpopulation of T cells. Cell surface expression pattern and immunoprecipitation studies indicated the molecule recognized by KuN241 to be complement receptor 1 (CR1). This was confirmed by sequential immunoprecipitation using E11, a CR1-specific monoclonal, and by immunoprecipitation analysis of a truncated transfection product of CR1. In vivo activation of PBLs for 7 days with pokeweed mitogen (PWM) abrogated surface expression of CR1 on B cells. Overnight culture with phorbol 12-myristate 13-acetate (PMA) downregulated the expression of CR1 detected by KuN241 both on PMNs and monocytes. Addition of MAb KuN241 to purified PMN and monocytes resulted in a transient increase in intracellular calcium ([Ca2+]i). This was blocked by the Fab fragment of MAb KuFc79 directed against the Fc gamma receptor. Further, Fab fragment of KuN241 cross-linked with F(ab')2 goat anti-mouse Ig failed to increase [Ca2+]i levels. Taken together, these results suggested a novel mechanism for transmembrane signaling events by dual binding of KuN241, the Fab region to CR1 and the Fc region of Fc gamma RII.

Animals↗

PubMed1995

Donor human leukocyte antigens in the circulation of liver allograft recipients.

Using a solid phase enzyme immunoassay (ELISA) with three different murine monoclonal antibodies (mAb) to HLA (human leukocyte antigens) framework determinants, circulating HLA were detected and quantitated both in normal individuals as well as liver allograft recipients. In normal individuals, the level of circulating HLA remained constant for several months of this study. The quantity of antigens present in the sera was not influenced by the collection procedures. During the immediate post-transplant period there was detectable donor HLA in the recipient's circulation; however, no correlation was noted between graft function and the large quantity of donor HLA present in the sera. Within 5 months after transplantation there was a gradual decrease in the amount of circulating HLA compared to the level seen in normal individuals. These shed donor antigens may play an active role in initiating the development of tolerance to the transplanted organ.

Blood Donors↗