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Biomedical subjects

G D Brown

Publications and source records attributed to G D Brown.

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

Suppression of local intestinal immunoglobulin A immune response to cholera toxin by subcutaneous administration of cholera toxoids.

Cholera toxin has been shown to modulate immune responses, generally producing enhancement when administered simultaneously with antigen and suppression when administered a day or more earlier. In a previous study using chronically isolated ileal loops in rabbits, we found that two subcutaneous (s.c.) "priming" and "boosting" doses of biologically active cholera toxin suppressed the local intestinal immunoglobulin A response to intraloop doses of cholera toxin. In the study reported here, two different biologically inactive but antigenically intact cholera toxoids, glutaraldehyde toxoid and choleragenoid, where administered s.c. by the same immunization schedule as for toxin in the earlier experiment. Suppression of local immune response to intraloop cholera toxin as compared with animals receiving no s.c. inoculations was again found. The results suggest that in this model suppression was immunological (mediated by an immunological mechanism) rather than toxigenic (mediated by biological activity of cholera toxin). In addition, the occurrence of suppression of local intestinal immune response after systemic immunization suggests that suboptimal protection against enteric infections could occur after s.c. vaccination.

Antibody Formation↗
PubMed1978

Local (immunoglobulin A) immune response by the intestine to cholera toxin and its partial suppression with combined systemic and intra-intestinal immunization.

Chronically isolated Thiry-Vella (T-V) ileal loops in rabbits were used to study the local and systemic immune response to purified cholera toxin (CT). Immunization consisted of intraloop (i.l.), subcutaneous (s.c.), or combined i.l. and s.c. inoculation of CT. Fluid from the loops and sera were tested for neutralization of CT by the blueing test and for relative content of isotype-specific (immunoglobulins A [IgA] and G [IgG]) anti-CT. To demonstrate protection against CT, fluid production by the chronic T-V loops was measured after challenge with CT; an "acute" loop prepared from adjacent intestine at the time of challenge was also tested in some animals. The highest neutralizing titers in loop fluids were found in animals receiving i.l. or i.l. and s.c. inoculations, whereas titers in sera were highest in rabbits receiving s.c. or i.l. and s.c. inoculations. IgA anti-CT in fluids became greatest after i.l. inoculation alone and was lowest in s.c. animals. Combined s.c. and i.l. immunization was accompanied by reduced content of IgA anti-CT in fluids as compared with that obtained with i.l. inoculation alone. This finding strongly suggested a suppressive effect on local immunization by s.c. inoculation. While this suppression may have been due to a direct (toxigenic) effect of CT on lymphocytes, an immunogenic mechanism, probably mediated through suppressor T cells, is favored. Little IgG anti-CT was detected in any loop fluids, but high levels were found in sera after two s.c. inoculations or four i.l. inoculations. Neutralization titers for the fluid specimens showed much better correlation with IgA anti-CT values than with IgG anti-CT values. The chronic and acute T-V loops showed protection against fluid production after exposure to CT in systemically and locally immunized animals. However, IgG anti-CT usually appeared in both loops; leakage of serum antibodies because of surgical manipulation was felt, therefore, to invalidate these protection results as a demonstration of local immunity. In challenge studies in undisturbed chronic loops, only local immunization alone was found to result in definite protection.

Animals↗
PubMed1975

Atrophy of villi with hypertrophy and hyperplasia of Paneth cells in isolated (thiry-Vella) ileal loops in rabbits. Light-microscopic studies.

Thiry-Vella loops in rabbit ileum were prepared by a new technique and were studied 18 hr to 49 days postisolation. The loops became grossly shortened after 14 days. Histologically, some shortening and blunting of villi was detectable as early as 4 days postisolation, and with prolonged isolation the changes became marked. Reduction in epithelial cell height and in brush border thickness were noted, and goblet cells were increased somewhat in size and prominence. Yet there was only slightly increased chronic inflammation in the mucosa and acute inflammation was uncommon, suggesting that mucosal injury was minimal. Furthermore, mean epithelial mitotic indices for the crypts did not rise and were generally reduced. Striking hyperplasia and hypertrophy of Paneth cells associated with mitotic figures in Paneth cells accompanied the atrophic changes in the villi. Reimplantation of loops into the bowel 3 weeks after isolation led to complete reversal of all changes, including hyperplasia of Paneth cells. On the other hand, regular perfusion of loops with a solution containing a large variety of nutrient substances failed to reverse the mucosal changes. It was concluded that atrophy of villi in isolated ileum of the rabbit occurred mainly because one or more substances contained in the chyme are needed to maintain normal mucosal architecture. These substances probably help regulate epithelial cell turnover and may well be endogenous in origin. Loss of substances in the chyme after loop isolation may also have led to Paneth cell hyperplasia. Alternatively, the Paneth cell changes and atrophy of villi might have been related in a cause and effect way.

Animals↗
PubMedDate not supplied

In vivo stimulation of H-2Dd expression following RadLV infection of thymocytes: increased transcription and DNA-binding activity to sequences 5' of the Dd gene.

Early studies showed that resistance to RadLV-induced leukaemia is mediated by gene(s) in the H-2D region of the MHC. Furthermore, these experiments correlated disease resistance with changes in H-2 expression occurring very early after virus inoculation. In the present study, we have begun to study at the molecular level this stimulation of H-2Dd class I expression in thymocytes of resistant mouse strains following infection by RadLV. The resistant strain of B10.T(6R) mice is used in these studies. When these infected thymocytes are assayed by fluorescence-activated cell sorting analysis, we can detect increased levels of H-2Dd expression on the surface of the thymocytes as early as 12 days following intrathymic injection of RadLV. RNA was prepared and examined by Northern blot analysis; H-2 mRNA levels are shown to be elevated on the order of four-fold. Nuclei were prepared from normal and infected thymocytes and the run-off transcripts were analysed by slot-blot hybridization. The rate of H-2 mRNA transcription is shown to be two- to three-fold higher in RadLV-infected thymocytes at 14 days post-infection when compared to that of normal thymocytes. These data demonstrate that elevation of H-2 surface expression following RadLV infection is the result of transcriptional activation. Extracts have been prepared from both normal and infected B10.T(6R) thymocytes and have been used in gel mobility assays in order to detect the interaction of potential trans-acting regulatory factors with sequences 5' of the H-2Dd gene. Specific binding occurs in both extracts, but the assay shows that the extracts differ both quantitatively and qualitatively; the extracts from infected thymocytes bind to additional sequences and to a higher degree than that from normal thymocytes. DNase I protection analysis locates a number of protein-binding sites, some of which are protected by extracts of either origin and some of which are only protected by extracts from infected cells. Two of these sequences are similar to the previously recognized consensus recognition sequences for the binding of AP-1 and NF-chi B. Oligonucleotides have been synthesized for both the genomic sequences being protected from DNase I digestion as well the published consensus sequences. While the DNA-binding activity in infected thymocytes for both AP-1 and NF-chi B-binding sites is increased, the binding to the genomic "AP-1 like" binding site is activated to a considerably greater level.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗