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Biomedical subjects

B Charlton

Publications and source records attributed to B Charlton.

At least 55 records · Page 3Linked to original sources
PubMed1989

Tolerance to aggregated human IgG but not ovalbumin can be induced by concurrent administration of depleting or non-depleting anti-L3T4 monoclonal antibodies.

Tolerance to soluble antigens has previously been shown to occur in mice if anti-L3T4 monoclonal antibody (MoAb) is administered at the time of antigen exposure. The process of tolerance induction may require the depletion of L3T4+ cells or it may be due to down-regulation or negative signalling of L3T4+ cells. We compared the effects of L3T4+ cell depletion and L3T4 antigen blockade at the time of primary antigen challenge on long-term humoral responses. Anti-L3T4 MoAb GK1.5 (IgG2b) and H129.19 (IgG2a) were used to deplete or block, respectively, L3T4+ cells. Following a short course of MoAb and antigen challenge with both aggregated human IgG (ag-HGG) and ovalbumin (OVA) in each mouse, primary response titres to each antigen in both MoAb treated groups were approximately 1:10(2) compared with approximately 1:10(5) in control mice. Repeated antigen challenge significantly increased the anti-OVA titre in both MoAb treated groups and by 150 days they were similar to controls. However, anti-HGG titres did not increase significantly in either of the MoAb treated groups. Thus either depletion of peripheral L3T4+ cells, or blockade of the L3T4 antigen without depletion of peripheral L3T4+ cells, can invoke a state of long-term antigen-specific tolerance to some antigens. Why the effect is restricted to particular antigens, and the exact mechanisms of tolerance induction remain to be determined.

Animals↗
PubMed1989

An increase in the survival of murine H-2-mismatched cultured fetal pancreas allografts using depleting or nondepleting anti-CD4 monoclonal antibodies, and a further increase with the addition of cyclosporine.

Depletion of CD4+ T lymphocytes with monoclonal antibodies (mAbs) has been shown to prolong allograft survival in mice. In this study, two rat anti-CD4 mAbs, H129.19 and GK1.5, were administered either alone or in combination with cyclosporine (CsA) to recipients of MHC-mismatched (H-2k to H-2d) cultured fetal pancreas allografts to determine their effect on graft survival. When compared with control mice, splenic CD4+ cells of GK1.5-treated mice were depleted by greater than 95%, but in H129.19-treated mice no depletion of CD4+ cells occurred. Instead, rat Ig was present on the surface of CD4+ cells in H129.19-treated mice. Anti-CD4 therapy with either H129.19 or GK1.5 prolonged fetal pancreas allograft survival to a similar extent, but did not lead to indefinite survival. Blockade of the CD4 antigen by the mAb H129.19 was as effective as the depletion of CD4+ cells by GK1.5 in prolonging allograft survival. Rejection of grafts by day 28 posttransplantation occurred in the absence of CD4+ cells, as determined by both flow cytometric examination of spleen cells and immunoperoxidase staining of the graft site. CsA alone did not prolong graft survival, but its addition to either H129.19 or GK1.5 mAb treatment significantly increased the survival rate of grafts at 28 days compared with mAb treatment alone. These results suggest that CD4+ cell depletion is not essential for effective anti-CD4 mAb therapy--and, further, that CsA may have a direct inhibitory effect on CD8+ cells during allograft rejection.

Animals↗
PubMed1989

Prevention of cyclophosphamide-induced diabetes by anti-V beta 8 T-lymphocyte-receptor monoclonal antibody therapy in NOD/Wehi mice.

Walter & Eliza Hall Institute nonobese diabetic (NOD/Wehi) mice exhibit a low incidence of spontaneous diabetes mellitus, but one large dose of cyclophosphamide (CY) can lead to a rapid progression to overt diabetes. Macrophages and Lyt-2+ and L3T4+ cells have been demonstrated to be involved in beta-cell destruction in this model. The role of a specific subset of T-lymphocytes expressing a particular T-lymphocyte-receptor segment was examined in CY-induced diabetic NOD mice with a mouse anti-V beta 8 T-lymphocyte-receptor monoclonal antibody (F23.1). After administration of CY, only 4 of 51 treated mice became hyperglycemic compared to 23 of 47 untreated mice, 13 of 26 mice treated with an isotype-matched control ascites, and 4 of 6 mice given antibody-negative ascites. Insulitis was significantly reduced in the F23.1-treated group, and immunocytochemistry revealed the absence of V beta 8 expression on cells in the lymphoid organs and insulitis of these mice. This investigation revealed that V beta 8+ cells were implicated in CY-induced diabetes in NOD/Wehi mice.

Animals↗
PubMed1989

Cyclophosphamide-induced diabetes in NOD/WEHI mice. Evidence for suppression in spontaneous autoimmune diabetes mellitus.

Nonobese diabetic (NOD) mice spontaneously develop a lymphocytic infiltration of pancreatic islets (insulitis) that may progress to overt diabetes. Virtually all NOD/WEHI mice develop insulitis, but very few progress to diabetes. However, cyclophosphamide (CY) can promote the onset of diabetes in NOD mice, including the NOD/WEHI strain. The means by which CY produces diabetes was investigated in NOD/WEHI mice, in which it was hypothesized that active suppression mechanisms prevented the progression from insulitis to diabetes. A study of the time course of insulitis in the islets after CY was given showed that insulitis was initially reduced but rapidly increased over 16 days, and T-lymphocytes were predominant in the lesion. This suggested a compression of the normal time course of the disease seen in NOD mice. CY did not produce diabetes in any of 11 non-NOD strains studied. Fetal isografts in NOD mice given CY several days before were subjected to lymphocytic infiltration and beta-cell destruction. These findings suggested that CY was not directly beta-cell toxic and that altered beta-cells were not essential for beta-cell destruction. This was further demonstrated with subdiabetogenic doses of streptozocin, which significantly damaged beta-cells but did not increase the severity of insulitis or induce diabetes as did CY. Most important, the transfer of mononuclear cells from nondiabetic NOD mice to mice given CY prevented diabetes, which indicated that the likely effect of CY was via immunomodulation, possibly by allowing poised effector cells to act on beta-cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Recurrence of insulitis in the NOD mouse after early prolonged anti-CD4 monoclonal antibody treatment.

The treatment of young NOD mice with continuous anti-CD4 mAb administration has previously been shown to prevent insulitis from developing. It has also been shown that insulitis, once present, can be abolished by anti-CD4 mAb treatment, but that the insulitis recurs after treatment stops. We have studied the effect of treating young NOD/Wehi mice with a limited course of anti-CD4 mAb to determine if any long term prevention of insulitis ensued. Anti-CD4 mAb (H129.19) was given i.p. weekly to 10 female NOD/Wehi mice from 25-100 days of age. Control mice received no treatment. The pancreas of the mice were examined histologically at 100 and 180 days of age and severity of insulitis graded from 0-100%. The insulitis grade in treated mice at 100 days was 5 +/- 2% compared with 29 +/- 26% in age matched control mice (p less than 0.01). At 180 days of age the insulitis grade in treated mice was 29 +/- 23% compared with 47 +/- 22% in aged matched controls (NS). Thus insulitis was prevented from developing by early treatment with anti-CD4 mAb but developed later when treatment was stopped. Early anti-CD4 mAb treatment does not therefore appear to produce a tolerant state so averting insulitis development and, insulitis can still develop in older NOD mice.

Animals↗
PubMed1988

Administration of silica particles or anti-Lyt2 antibody prevents beta-cell destruction in NOD mice given cyclophosphamide.

The cellular pathway of beta-cell destruction in type I (insulin-dependent) diabetes is still undefined. L3T4+ T-lymphocytes have a role in both the initiation of insulitis and in recurrent disease in transplanted allogeneic islets in nonobese diabetic (NOD) mice. The roles of macrophages and Lyt2+ T-lymphocytes in beta-cell destruction were studied in cyclophosphamide-induced diabetic NOD mice with silica particles and a rat anti-Lyt2 monoclonal antibody. After administration of cyclophosphamide, 10 of 26 untreated mice and 1 of 21 anti-Lyt2-treated mice became diabetic. Insulitis was significantly reduced in anti-Lyt2-treated mice, and immunocytochemical staining showed a lack of Lyt2+ cells. Only 1 of 19 silica-treated mice became diabetic, compared to 8 of 19 control mice. This study demonstrates that both Lyt2+ T-lymphocytes and macrophages are necessary, but not sufficient, for beta-cell destruction in NOD mice. Therefore, we propose that macrophages present beta-cell antigen to L3T4+ cells, which induce cytotoxic Lyt2+ cells to specifically destroy beta-cells.

Animals↗
PubMed1988

Progression from insulitis to beta-cell destruction in NOD mouse requires L3T4+ T-lymphocytes.

The identity of the cells responsible for beta-cell destruction in type I (insulin-dependent) diabetes is still uncertain. L3T4+ T-lymphocytes have a role in the initiation of insulitis and in damaging transplanted allogeneic islets in nonobese diabetic (NOD) mice. The role of L3T4+ T-lymphocytes in destruction of beta-cells of the NOD mouse was studied in cyclophosphamide (CY)-induced diabetic NOD mice with a rat anti-L3T4 monoclonal antibody (MoAb). After administration of CY, most untreated animals became diabetic, whereas all antibody-treated animals remained normoglycemic. Insulitis was still present in MoAb-treated animals, but immunocytochemical staining showed rat antibody blocking the L3T4 antigen on T-lymphocytes. This study provides further evidence that L3T4+ T-lymphocytes are critical to the process of beta-cell destruction in NOD mice. The means by which L3T4+ cells exert their effect remains to be clarified.

Animals↗
PubMed1988

A comparison of the effects of plasma exchange and immunoadsorption on anti-insulin antibody synthesis in rabbits.

Plasma exchange (PE) and ex vivo immunoadsorption (IA) may be applicable to the removal of anti-insulin antibodies (AI-Ab) from diabetic patients. However, the removal of antibodies may prompt an increase in their rate of synthesis and an overshoot of antibody levels which may be deleterious to the patient. The effects of both PE and IA on AI-Ab synthesis were studied in a rabbit model. Rabbits were immunized with insulin and the resulting AI-Abs removed by both plasma exchange and specific immunoadsorption. Following AI-Ab removal by PE no increase in AI-Ab synthesis or antibody overshoot occurred. However a large increase in AI-Ab synthesis and overshoot occurred following specific AI-Ab removal by immunoadsorption. Despite similar reductions in AI-Ab levels by PE and IA, no increase in antibody synthesis occurred due solely to antibody removal. It is likely that antigen released from the immunoadsorbent stimulated the increase in antibody synthesis following immunoadsorption. These findings are relevant to the clinical application of both PE and IA.

Animals↗
PubMed1986

Order of class III genes relative to HLA genes determined by the haplotype method.

The B18 C4A3 C4BQ0 BfF1 DR3 haplotype was found to be ideal for determining the order of C4 and Bf relative to HLA-B and DR by the haplotype method. All the copies of this haplotype are assumed to be derived from a single ancestral haplotype. Sixteen of the twenty-six BfF1-containing haplotypes carried all of the alleles from this "ancestral" haplotype. Most of the other BfF1-containing haplotypes could be derived from the "ancestral" haplotype by a single crossover event for one of the two possible gene orders. This suggests that B18 C4A3 C4BQ0 BfF1 DR3 is the sole source of the BfF1 allele. The uncommon C4 type on B18 C4A3 C4BQ0 BfF1 DR3 facilitates recognition of the BfF1-containing products of recombination between Bf and C4. One such recombinant haplotype was found which shows that the orientation of the class III genes is as follows: C4 is closest to HLA-B and Bf is closest to HLA-DR. This gene order is supported by all the earlier unequivocal results obtained using the haplotype method (Olaisen et al. 1983, Marshall et al. 1984a). Combining these results with the information on class III genes obtained from overlapping cosmid clones (Carroll et al. 1984) and earlier mapping studies (Robson and Lamm 1984) shows that HLA-B is telomeric to 21B. C4B, 21A, C4A, Bf and C2 then follow 21B in that order covering 120 kb. HLA-DR is located further toward the centromere.

Chromosome Mapping↗
PubMed1985

Vascular access for extracorporeal therapy in the rabbit.

A technique allowing short-term blood access for extracorporeal therapy in rabbits is described. The technique utilizes silicone rubber cannulae and teflon vessel tips to construct an externalized carotid-jugular arteriovenous shunt. The insertion procedure takes 1 h and extracorporeal blood flows in excess of 10 ml/min are obtainable for up to 7 days. Blood flow may still be obtained following shunt clotting by insertion of smaller diameter catheters through the arterial cannula. This technique has been successfully used for extracorporeal therapy in rabbit disease models.

Animals↗
PubMed1985

The effect of extracorporeal antibody removal on antibody synthesis and catabolism in immunized rabbits.

Plasma exchange therapy is currently used to remove antibody from the circulation in a number of autoimmune diseases. It has been suggested that the decrease in antibody level may affect synthesis rate by the removal of inhibitory feedback. This would then cause a rapid rise in antibody levels to or beyond those prior to depletion. Based on this supposition immunosuppression is nearly always used concomitantly with plasma exchange to prevent the expected increase in synthesis rates. An assessment of the effect of specific antibody removal by immunoadsorption on synthesis and catabolic rates was undertaken to clarify the nature of the response. Rabbits were immunized to bovine serum albumin (BSA) injected with 125I-anti-BSA IgG and later underwent extracorporeal immunoadsorption with BSA-Sepharose. At least 60% of circulating anti-BSA-IgG was removed. Mathematical analysis of 125I-anti-BSA IgG and anti-BSA-IgG levels demonstrated a reduction in catabolic clearance following immunoadsorption. Conversely synthesis rate was not altered. No significant overshoot of anti-BSA-IgG beyond pre-removal levels occurred. Based on these findings it is postulated that an increase in antibody synthesis does not generally occur following plasma exchange. The rise in antibody levels seen following plasma exchange probably reflect a reduction of catabolism combined with an unchanged rate of synthesis.

Animals↗
PubMed1985

A new application of plasma exchange in insulin dependent diabetes mellitus.

An insulin dependent diabetic patient was resistant to all but central venous insulin administration. For this reason plasma exchange was tried and it restored insulin responsiveness. An anti-insulin IgG antibody was identified in the patient's plasma. Plasma exchange reduced antibody levels and these correlated with daily insulin requirements. Kinetic analysis of anti-insulin antibodies, however caused us to doubt that they were the sole cause of the problem. Although the mechanism remains unclear, plasmapheresis proved to be an effective method of treating this patient's insulin resistance.

Diabetes Mellitus, Type 1↗
PubMed1985

Analysis of immunoglobulin G kinetics in the non-steady state.

The effect of specific intravascular IgG depletion on IgG catabolism, generation, and intrabody transfer has been studied in rabbits. In contrast to previous studies, the radiolabeled IgG kinetics were analyzed in the non-steady state. A two-pool model was used to determine IgG distribution, catabolism, generation, and intrabody mass transfer after intravenous injection of 125I-IgG. Circulating IgG was then specifically removed by plasma perfusion through a Protein-A Sepharose column in an extracorporeal circuit. Based on the two-pool analysis, IgG catabolic clearance fell after IgG removal (1.0 ml/hr vs. 0.7 ml/hr), and mean generation rate was unchanged. Plasma levels rose 20 hours after IgG removal as a result equally of contributions from intrabody transfer and of generation. Model parameters from plasma 125I decay analysis overestimated plasma 125I levels in the first 24 hours after removal, although predicted endogenous levels corresponded well with experimental results over a 7-day period. Rapid intravenous infusion of a 7% body weight volume of saline solution during IgG removal resulted in 50% greater plasma levels of 125I-IgG 24 hours after removal. This indicated that an increased lymphatic flow had occurred, resulting in increased IgG transfer from the extravascular to the intravascular space. The two-pool model adequately describes circulating IgG levels after specific IgG removal. Catabolic clearance was found to be a function of IgG level, whereas generation does not appear to be similarly dependent. Both the two-pool model and saline infusion procedure may be applied directly to the planning and optimization of plasma exchange therapy regimens in human autoimmune disease.

Animals↗
PubMed1984

Theoretical estimation of punch velocities and displacements of single-punch and rotary tablet machines.

The speed of travel of punches during compaction by a Manesty F3 single punch and D3B Rotary punch tablet machine has been derived from machine dimensions, normal operating speeds and by consideration of the consolidation of a theoretical compact. The analysis may also be used for machines with other dimensions, operating at different speeds with other materials, but would require modification if the punch head design on the rotary machine differed significantly. Punch speeds at the beginning of the compression cycle were similar for the two types of machines, namely 10.36 and 10.24 cm s-1 for the single and rotary machines. The time to reach maximum compression and the total time of contact between punches and powder for the single punch machine was 0.1 s for a compaction force of approximately 40 KN. For the rotary machine operating at approximately the same force, these two parameters were found to be 0.052 and 0.083 s respectively. The additional contact time is associated with a period during which there is no vertical movement of the punch, providing a 'dwell' time of 0.0314 s when the powder is held at a constant volume.

Drug Compounding↗
PubMed1984

Kinetics of intravenous saline infusion and selective IgG removal in rabbits.

Selective removal of approximately 60% of the plasma immunoglobulin G (IgG) mass in conscious rabbits was studied and compared with similar procedures combined with intravenous saline infusions equal to 7.5% body weight. Plasma concentrations of 125I-IgG and endogenous IgG were employed in model analysis to examine if saline infusions could be used to shift IgG from extra- to intravascular pool, thereby making more protein available for removal by extracorporeal plasma treatment. After IgG removal, the fractional metabolic clearance and the extra- to intravascular transfer coefficient were 40-50% lower than before IgG removal, and model simulations indicated that this may be caused by IgG binding. Saline infusion resulted in 40% more IgG mass in plasma 24 h after treatment compared with procedures without saline. Model analysis indicated that the increased IgG mass in plasma after saline procedures could be explained by a three- to fourfold increase in lymphatic clearance. Crystalloid infusions may be a method to increase the efficacy of repeated plasma exchange treatment.

Animals↗