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Effect of Locally Administered Endotoxin on Regenerating Appendix Structure and Responses of Appendix Cells to Mitogens¹

From the Department of Microbiology, Yale University School of Medicine, New Haven, Connecticut 06510

Abstract

In adult rabbits subjected to appendicostomy and sublethal irradiation, there was almost total destruction of appendix follicle lymphocytes with relative preservation of appendix domes and thymus-dependent areas (TDA). Regeneration of follicles was very incomplete during a 21-day period of observation. Daily instillation of endotoxin (LPS) or of killed Escherichia coli into the appendix over a 7-day period or longer failed to enhance follicle regeneration but gave rise instead, to an obvious and marked stimulation of macrophages, which replaced the follicle lymphocyte population entirely in most rabbits. The response of appendix cells in culture to PHA was parallel to the relative proportion of cells in the TDA, as established histologically, and was therefore exaggerated in the instances where follicle macrophages were stimulated and follicle lymphocytes depressed.

This experimental situation (regeneration after x-ray) differs from the normal developmental pattern of the appendix in young rabbits because of the presence of a large preexisting population of macrophages, responsive to LPS stimulation from the lumen and capable of overwhelming normal lymphocytic function.

Footnotes

¹ This work was supported by United States Public Health Service Research Grants AI-06112 and AI-06455.

² On leave of absence from the Department of Microbiology, Facultad de Ciencias Medicas, Universidad Nacional de Cuyo, Mendoza, Argentina.