F.B. de Brito

Drug effects on a novel model of connective tissue breakdown

Production of a granulomatous tissue adjacent to cartilage implants in subcutaneous tissues of mice by prior wrapping of cartilage with cotton, induces matrix depletion and a rise in serum levels of the acute phase protein haptoglobin. The granulomatous reaction to cotton could be inhibited partially, following treatment of mice with indomethacin, dexamethasone and cyclophosphamide but only the latter two reduced cartilage matrix loss.d-penicillamine was inactive. Regarding the acute phase response, dexamethasone andd-penicillamine appeared to lower and indomethacin and cyclophosphamide to elevate, serum levels of haptoglobin, but these effects were not statistically significant.

Polyarthritis and the air pouch reaction: dissimilarity of adjuvant and collagen models

The formation of an air pouch in the subcutaneous tissues of a rat previously inoculated intradermally with Freunds mycobacterial adjuvant for the induction of arthritis, provokes a marked but transient inflammatory reaction in the cavity lining of the pouch. The dependence of this reaction on arthritis development was investigated. It was found that rats inoculated with mycobacterial adjuvant by subcutaneous or intraperitoneal injection failed to produce either a pouch reaction or develop arthritis. Intradermal injections of carrageenan, mycobacteria (M. tuberculosis in saline), Freunds incomplete adjuvant alone or containing Salmonella typhimurium lipopolysaccharide and Bordetella pertussis organisms or mycobacterial adjuvant containing egg albumin were also ineffective. Intradermal injections of type II collagen in Freunds incomplete adjuvant did induce arthritis but no pouch reaction; however, this could be elicited after direct challenge with antigen. Pretreatment of rats intraperitoneally with saline suspensions of mycobacteria or a moderate dose of cyclophosphamide prevented both the pouch reaction and arthritis developing to intradermal mycobacterial adjuvant. Pretreatment of rats with mycobacteria was without effect on type II collagen-induced arthritis. From the results of this study it would appear that the air pouch reaction and arthritis induced by adjuvant are directly associated. The inability of collagen to induce a similar reaction demonstrates a fundamental dissimilarity with mycobacterial adjuvant in its mechanism of production of arthritis.

Susceptibility of Two Colonies of Wistar Rats to Inflammation, with Particular Reference to Delayed Hypersensitivity

Two colonies of Wistar rats were tested for their abilities to produce delayed hypersensitivity reactions and other forms of inflammation. Tuck rats, which respond to dextran with an anaphylactoid reaction, produced delayed reactions to tuberculin protein and to ovalbumin in Freunds incomplete adjuvant. On the other hand, NELP rats which do not respond to dextran also produced delayed reactions to tuberculin protein, but only to ovalbumin when this was contained in Freunds complete adjuvant. Rats of both colonies responded to cotton pellet-induced inflammation, but the adult NELP rats showed resistance both to adjuvant-induced and to collagen-induced arthritis, as well as to the production of experimental allergic encephalomyelitis. NELP rats also showed a much greater reticulo-endothelial system phagocytic activity although antibody titres to sheep red blood cells and the mitogenic activity of concanavalin A and of lipopolysaccharide on spleen cells were similar in the two colonies of rats.

Delayed Hypersensitivity Reactions in Rats and Their Response to Clinical Dextran

Four colonies of rats were tested for their ability to produce adjuvant-induced arthritis, oxazolone contact hypersensitivity and the dextran anaphylactoid reaction. Tuck Wistar and Hooded Lister rats, both of which respond to dextran, showed disseminated inflammatory lesions after adjuvant and exhibited oxazolone sensitisation, regardless of the age of the animal. Spontaneously hypertensive rats, which at all ages respond to dextran, also responded to adjuvant and oxazolone but only when they were young; as they grew older, this response to these two agents diminished. Wistar NELP rats, which at all ages do not respond to dextran, responded to oxazolone; sensitivity to adjuvant, however, was maximal only in young animals. The link between the ability of rats to resist the dextran anaphylactoid reaction and their failure to respond to adjuvant with disseminated inflammatory lesions has not been confirmed.

Adjuvant polyarthritis and the pseudosynovitis

The cavity lining of a six day old subcutaneous air pouch in rats resembles normal synovium in morphology and responds in a comparable manner during development of polyarthritis. The ability of newly formed pouches (one and two days old) to respond similiarly to polyarthritogen was examined here. Positive macro and microscopic changes similiar to those seen in the six day old pouch were observed in rats previously inoculated with adjuvant. The intensity of some of these changes varied between pouches. The results of this study indicate that the adjuvant induced air pouch reaction does not depend on the presence of synovial-like lining for its production.

Susceptibility of cartilage to damage by immunological inflammation.

Injection of ovalbumin into subcutaneous air pouches prepared on the backs of rats previously sensitised to the antigen resulted in the induction of a small and transient accumulation of inflammatory fluid with a predominantly polymorph cell infiltrate. Challenge of pouches of appropriately sensitised rats with Bordetella pertussis vaccine, on the other hand, resulted in a larger and more prolonged accumulation of fluid and cells with a predominantly mononuclear presence. When intact homologous femoral head cartilage was implanted in these inflamed pouches proteoglycan loss was found to be not different from similar implants in non-inflamed pouches. Coating the cartilage with human heat-aggregated immunoglobulin G prior to implantation in air pouches was also found to be without effect on subsequent proteoglycan loss.

The Effects of Cyclophosphamide on Delayed Hypersensitivity in Rats

Pretreatment of Tuck Wistar rats with cyclophosphamide (100 mg kg-1) intraperitoneally prevents the development of adjuvant-induced arthritis, experimental allergic encephalomyelitis and the delayed skin reactions after ovalbumin and Freunds incomplete adjuvant. The resistance of these rats to these stimuli is similar to that found in untreated NR Wistar rats which are resistant to dextran. However, cyclophosphamide suppresses the responses of Tuck Wistar rats to collagen-induced arthritis and sheep red blood cell agglutination, stimuli to which untreated NR Wistar rats respond. Nevertheless, the reactions of Tuck animals to the purified protein derivative of M. tuberculosis, the skin sensitisation to oxazolone, and the development of the delayed reaction after ovalbumin and Freunds complete adjuvant remain unchanged after cyclophosphamide pretreatment. The results indicate the possible existence of two separate types of delayed hypersensitivity reactions.

Genetic susceptibility of rats to some forms of delayed hypersensitivity

The F1 generation, produced by mating Wistar rats from the Tuck colony which react to dextran (R rats) with Wistar rats from the NELP colony which do not react (NR rats) all responded to dextran with an anaphylactoid oedema reaction, and developed arthritis after adjuvant injections (AIA), but failed to show ovalbumin-induced delayed hypersensitivity reactions (OA) and experimental allergic encephalomyelitis (EAE). Back-crossing the F1 generation with NR rats produced animals, only half of which responded to dextran, though all the offspring reacted well to AIA, but poorly to OA and EAE. This confirms that resistance to AIA is not associated with resistance to dextran.