Monocyte Function in Rheumatoid Arthritis

Infections in the compromised host

The skin and/or mechanical factors, such as coughing, ciliary action or urine flow, along with phagocytes and humoral and cell-mediated immunity, help to protect the body from infection. In compromised patients, these mechanisms are impaired or bypassed, rendering patients susceptible to infection by opportunistic organisms (bacteria, mycobacteria, fungi, viruses, parasites). Mechanical barriers may be breached in patients with burns or indwelling catheters, in diabetics or cancer patients, and in parenteral drug abusers. Humoral or cell-mediated immunity may be suppressed in non-neoplastic patients following splenectomy, in diabetics, in alcoholics and in those with certain rheumatic disorders, as well as in patients undergoing haemodialysis or receiving steroids or immunosuppressive drugs. In cancer patients infection is often a cause of death, frequently occurring as a result of granulocytopenia, obstruction of natural passages, or suppression or dysfunction of humoral or cell-mediated immunity. Diagnosis of the infection may be difficult and expert advice should be sought. Treatment should be started before a conclusive diagnosis has been made, particularly in neutropenic patients since infections may be life-threatening.

Monocyte Fc receptor function in rheumatoid arthritis. Enhanced cell-binding of IgG induced by rheumatoid factors

Monocytes from 11 patients with rheumatoid arthritis and 10 control subjects were purified by countercurrent elutriation. Rheumatoid arthritis monocytes had more cell-associated IgG (P less than 0.001) and bound more 125I-labeled heat-aggregated IgG in vitro (P less than 0.02) than did monocytes from control subjects. Interaction of rheumatoid factor (RF) with monocytes was then investigated. Purified 125I-labeled IgM-RF and IgG-RF bound directly to monocytes from normal individuals. Furthermore, preincubation of normal monocytes with RF augmented subsequent binding of aggregated IgG to the cells. We conclude that monocyte-associated RF can enhance binding of IgG-containing immune complexes to the cells and can exaggerate the measured number of Fc receptors. Such cell-bound RF may affect clearance of immune complexes by the reticuloendothelial system in vivo.

Enhanced prostanoid release from monocytes of patients with rheumatoid arthritis and active systemic lupus erythematosus

In patients with rheumatoid arthritis high levels of prostaglandin E1 have been found in the joint fluid, and its increased production by adherent synovial cells and macrophages clearly supports the notion that this arachidonic acid metabolite is involved in the pathology of the disease. Besides its known inflammatory qualities and the suppressive effects on various lymphocyte functions prostaglandin E2 has proved to be an essential cofactor in the secretion of the lymphokine osteoclast activating factor. In this study we have discovered an enhanced release of prostaglandin E1 and thromboxane B2 from a subpopulation of blood monocytes from patients with rheumatoid arthritis and active systemic lupus erythematosus. No correlation between prostanoid release from monocytes and inflammatory activity of the disease was found. However, even monocytes from patients with early stage or mild inflammatory activity displayed a 'stimulated' arachidonic acid metabolism. In contrast only patients with active systemic lupus erythematosus showed in this respect comparable secretory activity or monocytes. Our findings may point to a possible pathogenic role of prostanoids in rheumatoid arthritis, which may also have some implication for the early diagnosis of this disease and for its differentiation from other chronic inflammatory rheumatic conditions.

Rheumatoid arthritis and chronic bronchial suppuration

Twenty-two patients with rheumatoid arthritis and severe chronic bronchial suppuration are described. In 11 patients the respiratory symptoms appeared after the onset of arthritis at an unusually late age. We discuss causes for the disease association, in particular the possibility that disease modifying drugs in rheumatoid arthritis may predispose to the development of chronic bronchial suppuration; such a possibility requires prospective investigation.

Enhanced bacterial phagocytosis by peripheral blood monocytes in rheumatoid arthritis

To assess the functional state of peripheral blood monocytes in rheumatoid arthritis, we have measured phagocytosis of Staphylococcus aureus and Proteus mirabilis in 48 patients and 28 controls. Using radiolabelled bacteria preopsonised in normal human serum we have demonstrated significantly enhanced uptake of both organisms by patients' monocytes: (Median % uptake Staph. aureus: patients = 35.8; controls = 19.3; p less than 0.001. Median % uptake P. mirabilis: patients = 32.3; controls = 19.8; p less than 0.01.) These results indicate that patients' monocytes exist in an activated state, which may be important in the pathogenesis of rheumatoid arthritis.

Depressed exocytosis by rheumatoid neutrophils in vitro

Polymorphonuclear leucocytes and monocytes have been isolated from the peripheral blood of patients with rheumatoid arthritis and healthy controls using Percoll gradient centrifugation. These cells have been tested for their ability to release superoxide anion and to undergo exocytosis following stimulation with heat-aggregated IgG. Monocytes from patients and controls react similarly in these assays but neutrophils from the patients release less beta-glucuronidase than do normal cells. This could not be related either to the expression of cell surface Fc receptors or to oxidative metabolism and does not appear to be an effect of the administration of non-steroidal anti-inflammatory drug therapy. It is suggested that rheumatoid neutrophils are not inherently defective but are less responsive to activation in vitro because of prior exposure to immune complexes in vivo.

Monocyte receptor function in patients with rheumatoid arthritis

Monocytes from patients with rheumatoid arthritis (RA), osteoarthritis (OA), and normal volunteers were studied for abnormalities of Fc and C3 receptor function. Monocytes from the majority of 22 patients with active RA showed enhanced E-rosette formation and Ea phagocytosis compared to monocytes from 20 normal volunteers and 10 OA patients, However, no significant differences in binding of EAC or uptake of iodinated aggregated gamma globulin were found among the 3 groups. Corticosteroid-treated RA patients exhibited significant depression of EA-rosette formation and phagocytosis. These results suggest that there is modulation of EA receptor function in monocytes from RA patients.