A. D. Sedgwick

Studies into the mode of action of non‐steroidal anti‐inflammatory drugs using a model of facsimile synovium

The effect of non‐steroidal anti‐inflammatory drugs on inflammation produced in the 6‐day old air pouch by carrageenan or calcium pyrophosphate crystals has been examined. The system is a very reproducible way of studying the cellular and vascular components of inflammation. Non‐steroidal drugs have different profiles of activity when tested on the inflammation produced with the two irritants. In general, however, the tested compounds showed similar activity on individual models.

Studies into the association between leucocyte accumulation and oedema formation

We have treated rats with methotrexate to reduce their circulating leucocyte numbers and in particular their polymorphonuclear leucocytes. Injection of zymosan, calcium pyrophosphate dihydrate crystals, carrageenan or dextran into rat pleural cavities induced leucocyte accumulation and oedema formation both of which were reduced by prior methotrexate treatment. The observation that the depletion of circulating leucocytes reduces both inflammatory cell accumulation and oedema formation suggests that these two processes are closely linked. In contrast treatment of animals with the anti-complementary agent K76COONa blocked leucocyte accumulation but had no effect on oedema formation indicating the two processes can occur independently. This conflicting data suggests that the association between leucocyte accumulation and oedema formation is complex.

The effect of therapeutic agents on cartilage degradation in-vivo

Implantation of minced autologous cartilage into inflamed air pouches in mice allows the study of therapeutic agents on both the inflammatory process and cartilage degradation. Non‐steroidal anti‐inflammatory agents were found to reduce cell accumulation in response to carrageenan, but were unable to prevent proteoglycan loss from cartilage. In contrast. d‐penicillamine had no effect on the inflammatory process but significantly reduced proteoglycan loss. Our findings suggest that the autologous cartilage transplantation model in the mouse may be useful for studying novel anti‐arthritic agents.

Studies on the ability of inflammatory exudate obtained from acute and chronic phases of the inflammatory process to promote leukocyte locomotion in vitro.

Using a modified Boyden chamber system, inflammatory exudates taken from the acute carrageenan pleural model and the chronic carrageenan air-pouch model were tested for their ability to promote leukocyte locomotion in vitro. Both exudates were able to induce polymorphonuclear leukocyte (PMN) and mononuclear leukocyte (MN) migration, suggesting that cell-specific chemoattractants are not responsible for the progression of the inflammatory process from the acute to the chronic phase. Checkerboard assays were used to establish whether the observed migration was in response to chemotactic stimulation and/or chemokinetic stimulation. Both acute and chronic exudates were able to induce MN chemotaxis and chemokinesis. Acute exudate was able to induce PMN chemotaxis and chemokinesis, but chronic exudate was only able to induce PMN chemokinesis. This may partly explain the predominance of MNs in chronic inflammation. However, our present in vitro results have failed to demonstrate that cell-specific chemoattractants are responsible for the in vivo observation that migration of polymorphonuclear leukocytes precedes the migration of mononuclear cells.

The transition from acute to chronic inflammation

The realization that many diseases exist in which a large portion of the tissue damage results from the infiammatory response itself (as in some non-toxic granulomatous reactions^—rheumatic and allergic reactions also fall into this category) has, in recent years, prompted considerable interest in the pathological aetiology and pharmacological control ofthe infiammatory process. There is little doubt that the continued accumulation of leukocytes and their continued release of dcgradativc enzymes and oxygen radicals, form the main part of this damage. It would therefore be of great importance to understand the mechanisms whereby an acute infiammatory response switches into chronicity. In our department we use the simple concept that acute infiammatory lesions are dominated by the polymorphonuclear (PMN) leukocyte and chronic lesions are dominated by the mononuclear leukocyte. This still remains a useful way of differentiating between two types of lesion. However, little is known ofthe way in which the initial accumulation in tbe injured tissue cf the PMN leucokyte, during the acute phase, becomes replaced by the mononuclear leukocyte as the lesion persists into chronicity. This cellular transition seems to occur whatever the injurious stimulus but exhibits differences in its rapidity of onset, the time taken for its completion and tbe number of cells involved. Although this phenomenon was observed during the early part of the twentieth century, it was Paz and Specter (1962) wbo proposed the following three broad possibilities to account for it. (i) Tbe migration of haematogenous monocytes occurs subsequent to that ofthe PMN leukocyte, (2) there is a delayed proliferation of tissue mononuclear leukocytes and (3) both cell types migrate concurrently with a difference in their relative rate of migration and their subsequent fate in the infiammatory lesion. Studies on subcutaneous and peritoneal inflanntmation in rats exposed to a variety of irritants suggested that the third proposal was the most likely. Tissue proliferation of mononuclear leukocytes made only a small contribution to the exudate mononuclear leukocyte pool. Concurrent emigration of both cell types was observed, with the PMN leukocytes being removed from the lesion at a relatively rapid rate. It was concluded by Paz and Spector that the disappearance of polymorphs from the lesion, coupled with the persistence and immobilization of the mononuclear leukocytes provided an adequate explanation for the delayed mononuclear leukocyte preponderance, despite botb cell types migrating concurrently. Hurley, Ryan and Friedman (1966) provided evidence supporting the alternative proposal

A hypothesis for the mode of action of anti-rheumatic drugs in a model of cartilage destruction

We have been using as a model rats and mice with air pouches which develop lining cells closely resembling synovium (Edwards et al 1982; Sedgwick et al 1983). These pouches when sufficiently mature, i.e. 6 days, will respond to a variety of stimuli both immune and non‐immune with long lasting exudates containing many migrated leucocytes (Sedgwick et al 1983, 1984a).

Immune Inflammation in Newly Developing Facsimile Synovia

The injection of air into the subcutaneous tissue of the back in rodents has previously been shown to induce a lining which closely resembles synovial lining tissue. Air pouches of different ages represent the developmental stages of such tissue. We have found that pouches of 1 day in age induced in animals previously sensitised with bovine serum albumin (BSA) respond with low numbers of infiltrating leucocytes and a small fluid exudate volume 4 h after challenge into the pouch with BSA. In contrast, 3- and 6-day-old pouch tissue when challenged with antigen responds with a greater influx of leucocytes and a larger fluid exudate. These findings suggest that the constituent make-up of the air pouch-lining tissue is important for the full expression of the inflammatory response.

Enhancement of colloidal clearance in normal rats by sodium diethyl dithiocarbamate (DTC)

Enhancement of colloidal clearance in normal rats is induced by sodium diethyldithiocarbamate, administered by the oral route. Enhancement is only observed after a lag period of greater than seven days. The study evidences the efficacy of oral administration of DTC and a weekly frequency of dosing in this clearance model.

Effect of a Lymphocyte-Derived Pro-Inflammatory Factor on Carrageenan Pleurisy in the Rat

An intravenous injection of a lymphocyte pro-inflammatory factor (LpIF), obtained from rat spleen, restored diminished fluid and cellular responses in carrageenan pleurisy in leucopenic animals. A similar filtrate of bone marrow cells had no restorative properties. Previous results from elsewhere indicated a single pro-inflammatory activity on the fluid component of inflammation. We propose that LpIF has a more significant effect by influencing both components of inflammation and suggest that the discrepancy may be due to the different models used.