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Biomedical subjects

J A Smit

Publications and source records attributed to J A Smit.

At least 19 recordsLinked to original sources
PubMed2000

Size-exclusion chromatography--multiangle laser light scattering analysis of beta-lactoglobulin and bovine serum albumin in aqueous solution with added salt.

The solution characteristics of beta-LGB (beta-lactoglobulin) and BSA (bovine serum albumin) are reported as determined by size-exclusion chromatography with on-line multiangle laser light scattering, differential refractive index and UV detection. The order of the three in series placed detectors as well as the interdetector volumes have been carefully pointed out. At concentrations below 2.5 mg/ml and at different values of pH the weight-average molecular mass of both proteins have been obtained. They indicate the appearance of monomers, dimers and higher order multimers. For beta-LGB the growth of self-associates could be observed at the isoelectric point over a period of days. The range of applicability of the method is discussed.

Biopolymers↗
PubMed1999

Definition and characterization of chicken Gal alpha(1,3)Gal antibodies.

BACKGROUND: The Gal alpha(1,3)Gal epitope is of interest as, in pig-to-primate xenotransplantation, it is the major target of naturally occurring human IgM and IgG antibodies, leading to hyperacute rejection. Human and Old World monkeys make anti-Gal alpha(1,3)Gal antibodies as they lack a functional gene and do not express Gal alpha(1,3)Gal. Interestingly, the cultured fibroblasts of some other species, such as chickens, have been reported also not to express Gal alpha(1,3)Gal--if this is true for other tissues, and chickens do not express Gal alpha(1,3)Gal antigen, then they would have anti-Gal antibodies--which could have diagnostic and therapeutic value, particularly as chicken antibodies do not fix mammalian complement. METHODS: Standard serological methods were used to characterize the antibodies. Several baboons received pig kidney xenografts that had been perfused with hyperimmune chicken anti-Gal antibodies. RESULTS AND CONCLUSIONS: We now demonstrate that chickens do not express Gal alpha(1,3)Gal on their red cells, leukocytes, or tissues, and that their serum contains large amounts of anti-Gal alpha(1,3)Gal antibodies. In addition, chickens could be immunized to produce high-titer, high-avidity antibodies (9.5x10(9) M(-1))--an avidity considerably greater than that of the Gal alpha(1,3)Gal binding lectin IB4 (2.9x10(8) M(-1)) or Gal antibodies in human serum (2.2x10(5) M(-1)). Chicken antibodies, obtained from both normal and immunized chickens, could block the in vitro cytolysis of pig endothelial cells or lymphocytes by human or baboon antibodies. However, such antibodies tested in vivo in pig-to-baboon xenotransplantation failed to block hyperacute rejection and, indeed, may have accelerated this.

Animals↗
PubMed1995

The differentiation of Staphylococcus aureus from other Micrococcaceae isolated from bovine mammary glands.

Haemolysin production, the slide coagulase test and the tube coagulase test were assessed for their capability to differentiate Staphylococcus aureus among other Micrococcaceae in 199 isolates from udders of cows in herds with a low bulk milk somatic cell count. The API-Staph test was used as a reference. Haemolysin production was less effective in identifying Staph. aureus among Micrococcaceae than a combination of other tests. Differences were found in the predictive values of results from diagnostic protocols in which the slide coagulase test was performed on all Micrococcaceae, or on beta-haemolysin-negative Micrococcaceae only. Diagnostic protocols in which haemolysin production was combined with the results of the other tests resulted in excellent diagnostic performance and a reduction in diagnostic procedures. Recommendations for routine Staph. aureus identification in bovine mastitis bacteriology are given.

Animals↗
PubMed1994

Nonspecific mixed lymphocyte culture inhibitory antibodies in sera of tolerant transplanted baboons conditioned with total lymphoid irradiation.

Pretransplant conditioning of baboons with total lymphoid irradiation allows long-term renal allograft acceptance in one third of the recipients. Brief additional immunosuppression was given to some animals, but always for less than 14 days after transplant. This enabled us to study mechanisms of graft tolerance in the absence of long-term, nonspecific drug immunosuppression. While 3 patterns of unresponsiveness were noted, this study concentrated on serum-mediated suppression. Eleven of 16 (69%) baboons destined to become tolerant to their grafts developed a nonspecific MLC inhibitory factor in their sera. In most animals it appeared within 3-5 weeks after transplantation and persisted over the period of study (91-793 days after Tx). The suppressor factor was absent in sera from 38 control animals and 8/9 rejectors. It was shown to be a low affinity IgG antibody that inhibited MLC by binding to stimulator cells, an effect that could be overcome by addition of rIL-2 to cultures. NK cell lysis, cell-mediated lympholysis, and polyclonal mitogenesis were unaffected. Antibody binding to purified baboon T cells could not be demonstrated, though binding to EBV-transformed B cells was readily shown. Our study shows that total lymphoid irradiation permits the generation of blocking antibodies directed against APCs as one mechanism of maintaining T cell unresponsiveness. These observations are consistent with the masking of ligands involved in antigen presentation or costimulation leading to a sustained state of autoenhancement.

Animals↗
PubMed1994

A simple model for estimating protein solubility in aqueous polymer solutions.

A simple scaling analysis of protein solubility in semi-diluted polymer aqueous solutions was derived based on the recent theoretical development of Abbott et al. on the interactions between protein spheres and entangled polymer coils and the experimental observations of Atha and Ingham on the polymer-induced protein precipitation. Both the hard-sphere nature of the protein and the flexibility of the polymer coils have been taken into account in the model. The experimental data can be fitted by using this model with physically reasonable values of the exponent. This approach may be useful in estimating protein solubilities in water in the presence of polymer from limited and usually costly experimental data.

Chemical Phenomena↗
PubMed1994

Sensitivity of baboon lymphocytes to cyclosporin A and FK 506: relative resistance of alloactivated cells to CyA.

The interspecies differences in CyA pharmacokinetics necessitate the establishment of optimal immunosuppressive doses in the baboon, especially as its use as host for preclinical xenografts is anticipated. We assessed the immunosuppressive effects of CyA and FK 506 on lymphocytes from chacma baboons, using human cells for comparison. At concentrations up to 100 mumol/l, neither drug was toxic to lymphocytes. FK 506 inhibited baboon and human lymphocyte proliferation and IL-2 synthesis equally. In contrast, approximately four times higher doses of CyA were needed to inhibit baboon lymphocytes responding to alloantigens. This may explain the inadequate immunosuppression of baboon graft recipients treated with clinically acceptable doses of CyA. We propose that CyA whole blood target levels of +/- 1500 ng/ml should be used in this species and we provide evidence that chacma baboons are able to tolerate such doses without nephrotoxicity.

Animals↗
PubMed1994

Inhibiting the repair of DNA damage induced by gamma irradiation in rat thymocytes.

This study assessed the ability of 11 established and potential radiosensitizing agents to retard the repair of radiation-induced DNA damage with a view to enhancing the immunosuppressive effects of in vivo lymphoid irradiation. The capability of irradiated rat thymocytes to repair DNA damage was assessed by an adaptation of the fluorimetric unwinding method. Three compounds, 3-aminobenzamide (3-AB), novobiocin and flavone-8-acetic acid (FAA), inhibited repair significantly. We also report the effect of low-dose irradiation combined with repair inhibitors on the relationship between DNA strand breaks, fragmentation, cell viability and use of nicotinamide adenine dinucleotide (NAD). DNA fragmentation was increased by 1 mM/1 FAA, 1 mM/l novobiocin and 50 microM/l RS-61443 within 3 h of incubation. The latter two compounds also proved cytotoxic. All three drugs augmented the effect of ionizing radiation on the use of NAD. Of the agents investigated, FAA showed the most promise for augmenting the immunosuppressive action of irradiation at nontoxic, pharmacokinetically achievable concentrations.

Animals↗
PubMed1993

Within-herd and between-herd variation in diagnosis of clinical mastitis in cattle.

In a set of data on farmer-observed clinical mastitis in cattle, all milk samples were scored with regard to milk color and milk texture (presence of flakes and viscosity). During a 1-year period, 1,106 milk samples were collected from 125 farms with a bulk milk somatic cell count < 150,000 cells/ml. The overall variation, the between-herd variation, and the within-herd variation of the scores were evaluated and compared with each other. Differences between farmers were found for the scores on the visual characteristics per sample. However, these differences were not related to the reported number of cases of clinical mastitis per year. It was concluded that the diagnostic capability of farmers whose herds had low somatic cell counts did not have a negative influence on the validity of farmer-observed clinical mastitis incidence. However, care should be taken in herds with a low frequency of cases.

Analysis of Variance↗
PubMed1992

Enhanced spontaneous and induced LAK function in baboons receiving total lymphoid irradiation (TLI).

TLI has potent immunosuppressive effects, but there is concern over its possible carcinogenic properties. The aim of the study was to assess to what degree TLI may compromise natural killer (NK) and lymphokine activated killer (LAK) cell function. There was a significant increase (P less than 0.0001) in both NK-cell function (measured against K562 targets) and spontaneous LAK-cell function (measured against DAUDI targets) in fresh blood lymphocytes throughout a course of 8 x 100 cGy fractionated TLI. This may be related to a three- and sevenfold increase, respectively, in CD16+ CD8- and CD56+ CD2- cell frequencies over the same period. Mitogen-induced interleukin 2 (IL-2) synthesis from blood lymphocytes was inhibited by up to 75% with as little as 100 cGy of TLI. Expression of IL-2 receptors on fresh lymphocytes did not vary and remained low. Therefore spontaneous LAK occurrence appeared to be triggered through an IL-2-independent pathway. The in vitro addition of IL-2 verified that cells retained their ability to respond to this lymphokine resulting in greatly enhanced induced LAK function. This was most probably mediated by CD56+ cells which were found to readily express IL-2 receptors upon mitogen stimulation. In conclusion, fractionated low-dose TLI appears to enhance MHC unrestricted immune surveillance in a manner independent of IL-2 production.

Animals↗