Liquefaction of solid caseous tuberculous lesions and the subsequent cavity formation are probably the most dangerous processes in the pathogenesis of human pulmonary tuberculosis. In liquefied caseum, the tubercle bacilli grow extracellularly for the first time since the onset of the disease and can reach such large numbers that mutants with antimicrobial resistance may develop. From a cavity, the bacilli enter the bronchial tree and spread to other parts of the lung and also to other people. Of the commonly used laboratory animals, the rabbit is the only one in which cavitary tuberculosis can be readily produced. This report is the first to describe and analyze the complete course of cavitary tuberculosis, produced by aerosolized virulent bovine-type tubercle bacilli in commercially available New Zealand white rabbits. After the inhalation of 220 to 880 bacillary units, all of the rabbits were overtly well until they were sacrificed at 33 weeks. After the inhalation of 3,900 to 5,800 bacillary units, half of the rabbits died of progressive tuberculosis between 5 and 9 weeks and the other half lived until they were sacrificed at 18 weeks. Pulmonary cavities developed in both low-and high-dose groups, some beginning as early as 6 weeks. Bacilli from primary cavities sometimes caused nearby secondary cavities, but more frequently, they ascended the bronchial escalator, were swallowed, and caused secondary tubercles in the lymphoid tissue of the appendix and ileocecal junction. Histologically, and by culture, the number of bacilli found in the liquefied caseum varied from many to comparatively few. Strong tuberculin reactions at 4 weeks after infection were associated with fewer primary lesions, while strong tuberculin reactions at 33 weeks were associated with more cavitary lesions. In the tuberculous granulation tissue surrounding caseous and liquefied pulmonary foci and cavities, we found many mature epithelioid macrophages that contained high levels of the proteinase cathepsin D. Therefore, cathepsin D probably plays a major role in the liquefaction of solid caseous material and in the subsequent cavity formation. MATERIALS AND METHODS Rabbits and the number of bacillary units they inhaled. We exposed Pasteurella-free New Zealand White rabbits to high and low doses of M. bovis

Activation of the microvasculature is a major component of the inflammatory response. During inflammation the vascular endothelium not only becomes more permeable to plasma proteins but also develops adhesion molecules that initiate the local immigration of leukocytes. We describe herein the in vivo changes in the three major vascular adhesion molecules during the development and healing of two types of rabbit dermal inflammatory lesions: (1) acute lesions produced in rabbits by the topical application of 1% sulfur mustard (SM, the military irritant/toxicant); and (2) chronic (immune-mediated) lesions produced in rabbits by intradermal injections of Mycobacterium bovis (BCG), the vaccine strain of tubercle bacillus. In each case, frozen tissue sections were made from lesions of various ages and stained immunohistochemically for von Willebrand (vW) factor to measure the total functional microvasculature. The sections were also stained immunohistochemically for the vascular endothelial adhesion molecules ICAM-1, ELAM-1 (E-selectin), and VCAM-1, and for the leukocyte ligands for ICAM-1: LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18). Infiltrating monocytes and lymphocytes expressed the LFA-1 ligand and infiltrating PMN expressed the MAC-1 ligand. The area of stained microvasculature per square millimeter of tissue section was determined with the use of a computerized image analyzer. Edema and cell infiltration spread apart the microvessels, changing the number of microvessels per square millimeter of tissue section. Three methods of assessing such changes are presented. In SM lesions, endothelial ICAM levels were decreased from normal by about 50% at 1 and 2 days (when the lesions reached their peak size) and returned to normal at 3 and 6 days (during the healing process). ELAM rose in peak SM lesions and remained high during healing. VCAM levels, however, were only elevated in the 6-day (almost healed) lesions. In BCG lesions the levels of endothelial ICAM and VCAM (and to a lesser extent ELAM) were increased at 9 days and remained so as the size of the lesions peaked at 23 days. During the healing phase at 37 days, the elevated ICAM and VCAM levels decreased but the slightly increased ELAM levels persisted. These findings indicate that ELAM plays a major role in acute inflammation and that VCAM and ICAM play major roles in chronic inflammation. VCAM is known to be monocyte and lymphocyte selective.

Developing and healing dermal inflammatory lesions were produced in rabbits by the topical application of dilute sulfur mustard (SM), the military vesicant. In tissue sections of such lesions, cells containing the mRNA of important cytokines were identified with in situ hybridization techniques. These cytokines were neutrophil attractant/activation protein-1 (NAP-1 (also called IL-8), monocyte chemoattractant (activating) protein 1 (MCP-1), interleukin 1 (beta) (IL-1 (beta)), and GRO (a growth factor and chemokine). Mononuclear cells (mainly macrophages and activated fibroblasts) contained the mRNA of all four of these cytokines. A higher percentage of cytokine-producing mononuclear cells (macrophages and activated fibroblasts) was present in lesions at 2 days (their peak size) than at 6 days, when they were almost healed. Granulocytes emigrated from the bloodstream, passed through the lesions, and were the major constituent of the protective crust. This sequence correlated with the distribution of cells able to produce NAP-1: At 2 days and 6 days, the mononuclears that contained messenger RNA for this granulocyte chemoattractant were found mainly in the upper part of the dermis. At 2 days and 6 days, cells containing the mRNA of IL-1, a primary cytokine, were also found predominantly in the upper dermis, i.e., nearest the site of injury. In contrast, mononuclears containing the mRNA of MCP-1 (a monocyte chemoattractant), and the mRNA of GRO (a granulocyte chemoattractant) were more equally distributed throughout the dermis. SM stimulated hair follicle epithelial cells to up-regulate GRO mRNA and, to a lesser degree, NAP-1 mRNA. Apparently, the irritation produced by SM directly or indirectly induces such epithelial cells to manufacture these growth factors. In the rabbit, hair follicles are known to be the main source of new epithelial cells after the covering epithelium has been destroyed. Therefore, GRO is probably a major autocrine-paracrine stimulus for such repair. A brief review of the role of cytokines in dermal inflammation is presented.

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We found that in contrast to (BXSB 9 NZB) F 1 female mice that spontaneously develop severe systemic lupus erythematosus (SLE), male (BXSB 9 NZB) F 1 mice are not prone to SLE, but instead develop seronegative ankylosing enthesitis in ankle/tarsal joints only when caged in groups, with the incidence reaching 83% at 7 months of age. This ankylosis is microscopically characterized by a marked proliferation of fibroblast-like cells positive for bone morphogenetic protein (BMP)-2 in association with heterotropic formation of cartilages and bones in hyperplastic entheseal tissues and subsequent fusion of tarsal bones. Elevated potentials of popliteal lymph node T cells producing interleukin (IL)-17 and interferon (IFN)-c were significantly associated with joint ankylosis, suggesting the involvement of these cytokines in effector phase mechanisms of the disease, including up-regulated BMP signaling pathways. There was no difference in serum autoantibody levels between affected and unaffected mice. Parental BXSB and NZB strains of both sexes did not develop the disease even when caged in groups, indicating that the disease develops under the control of susceptibility genes derived from both parental strains. These results indicate that (BXSB 9 NZB) F 1 male mice are a suitable model for clarifying genetic, environmental and molecular mechanisms underlying ankylosing enthesitis and related diseases.