Corticosteroids and the humoral immune response of mice i. Differential effect of corticosteroids upon antibody formation to sheep red blood cells in spleen and bone marrow

Bone marrow of NZB/W mice is the major site for plasma cells resistant to dexamethasone and cyclophosphamide: implications for the treatment of autoimmunity

Antibodies contribute to the pathogenesis of many chronic inflammatory diseases, including autoimmune disorders and allergies. They are secreted by proliferating plasmablasts, short-lived plasma cells and non-proliferating, long-lived memory plasma cells. Memory plasma cells refractory to immunosuppression are critical for the maintenance of both protective and pathogenic antibody titers. Here, we studied the response of plasma cells in spleen, bone marrow and inflamed kidneys of lupus-prone NZB/W mice to high-dose dexamethasone and/or cyclophosphamide. BrdU+, dividing plasmablasts and short-lived plasma cells in the spleen were depleted while BrdU- memory plasma cells survived. In contrast, all bone marrow plasma cells including anti-DNA secreting cells were refractory to both drugs. Unlike bone marrow and spleen, which showed a predominance of IgM-secreting plasma cells, inflamed kidneys mainly accommodated IgG-secreting plasma cells, including anti-DNA secreting cells, some of which survived the treatments. These results indicate that the bone marrow is the major site of memory plasma cells resistant to treatment with glucocorticoids and anti-proliferative drugs, and that inflamed tissues and secondary lymphoid organs can contribute to the autoreactive plasma cell memory. Therefore, new strategies targeting autoreactive plasma cell memory should be considered. This could be the key to finding a curative approach to the treatment of chronic inflammatory autoantibody-mediated diseases.

The effect of corticosteroids upon the number and organ distribution of "background" immunoglobulin-secreting cells in mice

The influence of the synthetic corticosteroid dexamethasone sodium phosphate (DEXA) upon the immunoglobulin (Ig)-secreting cells was studied in not intentionally immunized BALB/c mice. This was done for IgM-, IgG-, and IgA-secreting cells in spleen, mesenteric lymph nodes (MLN), and bone marrow (BM). A single injection of DEXA (16 to 144 mg/kg body wt) markedly reduced the number of Ig-secreting cells in spleen and MLN within 1 day, but hardly affected their number in the BM. The decrease was immediately followed by a recovery and, at the highest doses and especially in MLN, by an overshoot. Two weeks after the initial decrease a second decrease was found. When mice were subjected to daily treatment with DEXA during 1 week, initially a recovery pattern was found in spleen and MLN similar to that found after a single injection of a high dose. In this case, however, the effects were less dose dependent, and the overshoot reaction was followed by a period of subnormal numbers of Ig-secreting cells which lasted at least 1 week. This late effect of DEXA not only occurred in spleen and MLN, but also in the BM. The most prominent effect of daily treatment with DEXA was the long-lasting decrease of the number of IgG-secreting cells starting 1 week after withdrawal of treatment. This decrease was associated with a severely decreased serum IgG level.

The differential sensitivity of rat peripheral blood T cells to immunosuppressants: cyclophosphamide and dexamethasone

Peripheral blood T cells from rats given a single oral dose of dexamethasone (DMS) or cyclophosphamide (CY) exhibited a differential sensitivity to these compounds as measured by lymphoproliferation in the presence of concanavalin A (Con A) or phytohemagglutinin hemagglutinin (PHA). Con A-responsive cells (T Con A) were found to be resistant to the effects of DMS, while the PHA-responsive population (T PHA) showed a dose-dependent suppression at dose levels of 0.35 and 1.00 mg/kg. DMS did not alter serum antibody production against sheep erythrocytes at the dosage level which produced a significant depression of the PHA response. Animals treated with CY showed enhanced Con A-mediated lymphoproliferation at a dose of 15 mg/kg and marked suppression at 45 mg/kg. The PHA-mediated response, however, exhibited only a dose-dependent suppression at both dosage levels. CY had no effect on the antibody response at doses that enhance Con A lymphoproliferation. These results suggest that T helper cells and T suppressor cells are not TpHA cells.