Biomedical subjects

A M Nesbitt

Publications and source records attributed to A M Nesbitt.

5 recordsLinked to original sources

PubMed1999

Anti-major histocompatibility complex class II treatment prevents graft rejection in the hamster-to-rat cardiac xenograft.

BACKGROUND: Several groups have achieved graft acceptance in the concordant hamster to rat model by using a combination of anti-proliferative drugs and conventional immunosuppressive therapy. However, such aggressive treatment often leads to the recipient dying with a functional xenograft, as a result of opportunistic infections. This study aimed to investigate the effects of a short course of therapy with an anti-MHC class II monoclonal antibody treatment (chimeric OX6 [cOX6]) in combination with cyclosporin A (CyA) in a concordant hamster-to-rat xenograft model. METHODS: Rats receiving hamster cardiac xenografts were given CyA or cOX6 alone or in combination and were monitored daily to assess the effect of treatment on graft survival. Additional studies monitored the effect of treatment on the production of cytolytic anti-hamster antibodies by the recipient and the deposition of immunoglobulin (Ig)M and complement factors within the xenograft. RESULTS: Treatment with CyA only had no effect on graft survival, whereas treatment with cOX6 increased graft survival time by 2 days. The median graft survival time for cOX6+CyA was 76 days. cOX6 treatment of rats having undergone transplants inhibited the rise in cytotoxic anti-hamster antibodies in peripheral blood until day 5, whereas combination therapy completely inhibited anti-hamster antibody formation. Fluorescence-activated cell sorter analysis showed treatment with cOX6 significantly reduced circulating B cell numbers until day 5. Anti-MHC class II treatment also markedly reduced the deposition of both IgM and C3. Anti-MHC class II treatment with CyA gives long term survival in concordant xenografts without severe side effects. CONCLUSIONS: The mechanism of action of this combination is complex and could be caused by an initial inhibition of B cell function by the anti-MHC class II treatment and the subsequent inhibition of T cell dependent pathways by CyA.

Animals↗

PubMed1995

The N-terminal end of the CH2 domain of chimeric human IgG1 anti-HLA-DR is necessary for C1q, Fc gamma RI and Fc gamma RIII binding.

We have found that amino acid residues necessary for C1q and Fc gamma R binding of human IgG1 are located in the N-terminal region of the CH2 domain, residues 231-238, using a matched set of engineered antibodies based on the anti-HLA-DR antibody L243. Changing the leucine 235 in the CH2 region of IgG3 and IgG4 to glutamic acid was already known to abolish Fc gamma RI binding. We have confirmed this for IgG1 and also found a concomitant abolition of human complement lysis with retention of Fc gamma RIII-mediated function. Changing the glycine at 237 to alanine of IgG1 also abolished Fc gamma RI binding and reduced human complement lysis and Fc gamma RIII-mediated function. Exchanging the whole region 233-236 with the sequence found in human IgG2, abolished Fc gamma RI binding and human complement lysis and reduced Fc gamma RIII-mediated function of IgG1. In contrast, a change in the previously described C1q-binding motif, from lysine at 320 to alanine, had no effect on IgG1-mediated complement lysis.

Amino Acids↗

PubMed1990

Phenotypic changes in a CD4+ lymphocyte subset correlate with a conversion from suppressor to helper inducer function.

The monoclonal antibodies WR16 (CD45RA) and WR19 were used to isolate two reciprocal subsets of CD4 lymphocytes by negative selection. The CD4+/WR16-/WR19+ subset exhibited helper-inducer activity in a pokeweed mitogen (PWM)-driven Ig secretion assay, whereas the CD4+/WR16+/WR19- subset showed suppressor activity. When the CD4+/WR16+/WR19- subset was cultured in phytohaemagglutinin (PHA) or purified protein derivative (PPD) there was increased expression of the antigen binding WR19 but the cells remained WR16 negative. Cultures of CD4+/WR16+/WR19- lymphocytes with PHA or PPD induced a phenotypic change that resulted in a population which was CD4+/WR16-/WR19+. Investigation of the functional activity of the CD4+/WR16+/WR19- subset, before and after activation and phenotypic change to WR16-/WR19+, indicated that the change in phenotype correlated with a functional conversion from suppressor to helper-inducer activity. These results suggest that the CD4+/WR16+/WR19- suppressor subset comprises cells that differentiate to WR16-/WR19+ helper-inducer cells after exposure to antigen or mitogen.

CD4 Antigens↗

PubMed1987

Functional heterogeneity of CD4+ T lymphocytes: two subpopulations with counteracting immunoregulatory functions identified with the monoclonal antibodies WR16 and WR19.

Monoclonal antibodies (MoAbs) WR16 and WR19 bound to 47% and 43% of CD4+ tonsil T lymphocytes, respectively. WR16 immunoprecipitated a 220,000 molecular weight (MW) component that was also expressed on CD8+ lymphocytes and on B lymphocytes, whereas binding of WR19 was restricted to CD4+ lymphocytes. Binding of these two MoAbs on freshly prepared tonsil CD4+ T lymphocytes was mutually exclusive, and they were used to prepare reciprocal CD4+ subpopulations by negative depletion using the panning technique. Recombination of subsets isolated in this way with autologous B lymphocytes activated with pokeweed mitogen demonstrated that WR16+/OKT4+ lymphocytes suppressed B lymphocyte Ig secretion, whereas WR19+/OKT4+ lymphocytes helped B lymphocyte Ig secretion. Removal of WR16+ cells from a CD4+ helper cell population enhanced B lymphocyte Ig secretion rate, whilst the re-addition of WR16+ cells to WR19+ helper cells reduced B lymphocyte Ig secretion rates to that seen with non-fractionated CD4+ helper cells. The overall level of helper activity induced by a given CD4+ population was thus a consequence of an interaction between WR19+ helper cells and WR16+ suppressor cells. The WR16+ subset of CD4+ cells exhibited a greater proliferation rate than WR19+/CD4+ cells in response to mitogen. Proliferation of negatively selected WR16+/CD4+ lymphocytes was inhibited by pretreatment with WR16, which also induced a concomitant increase in the level of suppressor activity of these cells. Expression of the antigens identified by these two MoAbs was not constant as phytohaemagglutinin activation of T lymphocytes induced a loss of WR16 binding with a simultaneous increase in the level of WR19 bound/cell and in the proportion of WR19+ cells. T lymphocyte clones selected from a normal population were composed of a disproportionately high number positive for WR19 and negative for WR16. These data indicated that the absence of the WR19 antigen on WR16+ cells may be transient as the antigen was acquired by the majority of CD4+ T lymphocytes after activation. These two MoAbs may therefore be used to predict the functional status of a heterogeneous population of CD4+ lymphocytes and may also prove to be of use in the study of CD4+ T lymphocyte activation.

Antibodies, Monoclonal↗

PubMed1986

Identification and isolation of OKT4+ suppressor cells with the monoclonal antibody WR16.

The monoclonal antibody WR16 was secreted by a hybridoma produced by fusing splenocytes from a BALB/c mouse immunized with human T-cell chronic lymphocytic leukaemia cells and the murine myeloma cell line NS-O. WR16 reacts specifically with human lymphocytes and binds to 48% of OKT4+ T lymphocytes and the majority of B lymphocytes. Human OKT4+ tonsil lymphocytes were subfractionated into WR16-/OKT4+ and WR16+/OKT4+ subpopulations by the panning technique. The capacity of these cells to help or suppress pokeweed mitogen-induced immunoglobulin (Ig) secretion by autologous B lymphocytes was monitored after 9 days of coculture. Cells of phenotype WR16-/OKT4+ enhanced Ig secretion in excess of that found with non-fractionated OKT4+ lymphocytes, whilst WR16+/OKT4+ lymphocytes suppressed Ig secretion when added to a mixture of B lymphocytes and non-fractionated OKT4+ cells. The WR16-/OKT4+ subpopulation was further fractionated by use of the MoAb Leu 8. Forty-two percent of WR16-/OKT4+ lymphocytes bound Leu 8, and cells of the phenotype WR16-/OKT4+/Leu 8+ were found to induce B-lymphocyte Ig secretion, whilst WR16-/OKT4+/Leu 8- lymphocytes were less active in this system. These data confirm the heterogeneity of the human T helper/inducer subset and indicate the existence of a population of OKT4+ lymphocytes that can suppress Ig secretion in the absence of OKT8+ lymphocytes.

Antibodies, Monoclonal↗