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J C Howard

Publications and source records attributed to J C Howard.

At least 109 records · Page 6Linked to original sources
PubMed1979

The role of subregions of the rat major histocompatibility complex in the rejection and passive enhancement of renal allografts.

The laboratory recombinant haplotype H-1acl of the Norway rat has been used in studies of the rejection and passive enhancement of kidney allografts. While the full H-1a haplotype provoked acute rejection, neither of the isolated subregions, H-1Aa and H-1Ba, did so. It was also found that alloantisera raised against either the H-1Aa or the H-1Ba antigens would enhance the grafts. It is suggested that both MHC subregions contain a histocompatibility locus (i) for kidney (as they do for skin) and that in the genetic combinations studied only incompatibility for both provokes a response sufficient for rejection. In other combinations, however, single region incompatibilities may be sufficient.

Animals↗
PubMed1978

Primary in vitro antibody formation in the rat: partial characterization and properties of an inhibitor cell present in normal spleen.

Rat spleen cells are shown to be unresponsive to sheep red cells (SRBC) in vitro under conditions in which thoracic duct lymphocytes (TDL) respond very well. By adding unresponsive spleen cells to responsive TDL cultures, the spleen cells are shown to contain an inhibitor capable of preventing the response to SRBC. The inhibitory activity is a property of live cells; it is sensitive to radiation doses as low as 100 R x rays and to mitomycin C. It can be completely removed from spleen cell suspensions by extraction with large amounts of carbonyl iron or by filtration through nylon wool columns. It is less efficiently removed by filtration through Sephades G-10 columns, and is completely resistant to the cytotoxic effects of silica. From a practical point of view, extraction of a spleen cell suspension with carbonyl iron is a useful method of obtaining fully responsive lymphocyte populations from rat spleen.

Animals↗
PubMed1978

Protein dissociation from DNA in model systems and chromatin.

Salt induced dissociation of protamine, poly(L-lysine) and poly(L-arginine) from DNA was measured by relative light scattering at theta = 90 degrees and/or centrifugation. Dissociation of histones from DNA was studied using relative light scattering and intrinsic tyrosine fluorescence. Protamine was dissociated from DNA at 0.15 M MgCl2 (ionic strength mu = 0.45) or 0.53 M NaCl (mu = 0.53) based on light scattering data and at approximately 0.2 M MgCl2 (mu = 0.6) or 0.6 M NaCl based on centrifugation data. NaCl induced dissociation of poly(Lys) or poly(Arg) from natural DNAs measured by light scattering did not depend on the guanine plus cytosine content. To dissociate poly(Arg) from DNA higher ionic strength using NaCl, MgCl2, or CaCl2, similar ionic strength using NaClo4, and lower ionic strength using Na2SO4 was needed then to dissociated poly(Lys). Both the decrease in light scattering and the enhancement of tyrosine fluorescence of chromatin occurred between 0.5 and 1.5 M NaCl when histones were dissociated.

Anions↗
PubMed1977

The acylation of bovine serum albumin with diacetylcycloserine.

The reaction of the amino groups of bovine serum albumin (BSA) with diacetylcycloserine (I) at pH 7.2-9.0 proceeded with both acylation by the diacetyl-beta-aminooxy-D-alanyl (DAA) group and acetylation. The number of DAA groups was determined by their conversion to cycloserine (III) which can be accurately measured in micromolar amounts. The method was developed using the model compound diacetyl-beta-aminooxy-D-alanine butyl amide (II) which was converted to beta-aminooxy-D-alanine butyl amide (IV) by methanolysis and then to cycloserine by basic ring-closure of IV. Calculations using results obtained by this method combined with the experimentally determined number of free amino groups in the modified BSA indicated that the reaction of excess I with BSA effected the acetylation of about 35 and the acylation with DAA groups of about 22 of the 59 amino groups. These findings were supported by experiments demonstrating that the amount of acetic acid formed by hydrolysis of the modified BSA was approximately that predicted from the results of the cycloserine analyses.

Acetylation↗
PubMed1976

SPECIFIC positive and negative selection of rat lymphocytes reactive to strong histocompatibility antigens: activation with alloantigens in vitro and in vivo.

This study compares the functional properties of rat thoracic duct lymphocytes (TDL) after stimulation with strong alloantigens of the major histocompatibility complex (MHC) either in vitro in preparative mixed lymphocyte interactions (MLI) or in vivo in systemic graft-vs-host (GVH) reactions. Comparisons were made of PHA responses and reactivity to the specific priming haplotypes or to third party haplotypes in analytical MLI and in GVH reactions either before or after the activated populations were "parked" in syngenetic T cell-deprived (B) rats. These comparisons can be summarized as follows: 1) TDL populations primed in bulk MLI cultures (MLI-TDL) slowed some evidence of specific positive selection when tested immediately; MLI responses to specific alloantigens were both relatively large and accelerated in tempo, whereas responses to third party alloantigens were diminished but also accelerated in tempo. Specific GVH responses were more marked than in third party recipients but they were also decreased relative to normal, and displayed an abberant dose/response slope. MLI-TDL populations tested after they had been stored in syngeneic B rats showed clear evidence of stable-specific positive selection; specific MLI and GVH responses were enriched relative to third party responses and also in comparison to normal, unselected TDL populations. This finding indicates that GVH and MLI reactivity are probably both functional capacities of the same lymphocyte subpopulation since positive selection by one function (MLI) also enriched for a second (GVH). 2) Parental strain TDL activated in vivo in the systemic GVH reaction in irradiated F1 animals and recovered from the thoracic duct 3 to 4 days later (late GVH-TDL) consisted mainly of blast cells, however, in contrast to MLI-TDL these populations showed no evidence of positive selection when tested before or after parking in B rats. MLI responses to specific alloantigens were minimal, and greatly reduced in magnitude compared to normal. GVH responses to specific haplotypes could be detected, but these were not enriched compared to normal, despite the content in the late GVH-TDL populations of a significant proportion of blast cells presumably activated by host alloantigens. 3) Early collections (less than 40 hr) of parental strain GVH-TDL collected from F1 recipients contained no blast cells and showed impressive degrees of negative selection; they were markedly depleted of both GVH and MLI activity to specific alloantigens but displayed normal reactivity to third party alloantigens. Moreover, specific negative selection was persistent in these populations parked for several weeks in B rats, and indication that a specific subpopulation of reactive cells had been physically eliminated. 4) PHA responses of both MLI- and GVH-activated TDL populations tested either before or after parking in B rats were approximately normal on a per T cell basis...

Animals↗
PubMed1976

Specific selection of cytotoxic effector cells: the generation of cytotoxic T cells in rat thoracic duct lymphocyte populations positively or negatively selected for reactivity to specific strong histocompatibility alloantigens.

These studies consider the generation of cytotoxic T lymphocytes (CTL) from precursors (CTLP) present in rat thoracic duct lymphocytes after stimulation with strong alloantigens. Also, they explore the relationship between CTLP and "initiator" (I) lymphocytes responsible for specific GVH and MLI reactions. Positively selected TDL populations prepared in bulk MLI cultures show enriched GVH and MLI reactivity for the selecting major histocompatibility complex (MHC) haplotype, but no cytotoxic activity, raising the possibility that I and CTLP may belong to different subpopulations, and the latter failed to differentiate or to survive under these culture conditions. Restimulation of these cells in Marbrook culture vessels with the original priming haplotype under conditions suitable for generating killer cells in vitro resulted in greatly increased specific CTL activity with accelerated kinetics soon after priming and normal kinetics later. These findings indicate that "memory" killer cells can be generated in a previously stimulated lymphocyte population that had no overt cytotoxic activity. Restimulation with third party haplotypes failed to give CTL activity either to specific or to third party targets. Negatively selected TDL populations prepared by "filtration" through x-irradiated F1 rats, depleted of specific GVH and MLI responses, were also depleted of the ability to generate CTL in Marbrook cultures stimulated with the selecting haplotype. Stimulation with third party haplotypes, or with both third party and specific haplotypes together, gave CTL effective only against the third party target.

Animals↗