Lymphocyte corticosteroid-mediated

As mentioned previously, glucocorticoids promote apoptosis and reduce survival, differentiation, and proliferation of a number of inflammatory cells. While there is an increase in the number of polymorphonuclear leukocytes in the circulation, corticosteroids cause the involution and atrophy of all lymphoid tissue and decrease the number of circulating lymphocytes. The striking lymphocytopenia is caused in large part by an inhibition of lymphocyte proliferation, although diminished growth with preferential accumulation of cells in the Gi-phase of the cell cycle is followed by cell death. These effects are mainly mediated by alterations in cytokine production and action. 

Corticosteroids have been used to treat asthma since 1950 and are presumed to act by their broad anti-inflammatory efficacy, mediated in part by inhibition of production of inflammatory cytokines (see Chapter 39). They do not relax airway smooth muscle directly but reduce bronchial reactivity and reduce the frequency of asthma exacerbations if taken regularly. Their effect on airway obstruction may be due in part to their contraction of engorged vessels in the bronchial mucosa and their potentiation of the effects of 13-receptor agonists, but their most important action is inhibition of the infiltration of asthmatic airways by lymphocytes, eosinophils, and mast cells. 

Treatment with omalizumab, the monoclonal humanized anti-IgE antibody, is reserved for patients with chronic severe asthma inadequately controlled by high-dose inhaled corticosteroid plus long-acting B-agonist combination treatment (eg, fluticasone 500 meg plus salmeterol 50 meg inhaled twice daily). This treatment reduces lymphocytic, eosinophilic bronchial inflammation and effectively reduces the frequency and severity of exacerbations. It is reserved for patients with demonstrated IgE-mediated sensitivity (by positive skin test or radioallergosorbent test [RAST] to common allergens) and an IgE level within a range that can be reduced sufficiently by twice-weekly subcutaneous injections. 

The role of both T and B lymphocytes in a variety of disease states beyond transplantation has become increasingly important in the past decade. This is especially true of those diseases frequently referred to as autoimmune in their etiology, such as rheumatoid arthritis, nephrotic syndrome, systemic lupus erythematosus, inflammatory bowel disease, and so on. In addition, several other major diseases are also known to have a component of T- or B-cell-mediated pathogenesis, for example, atopic dermatitis, psoriasis, and asthma. Until very recently, the mainstay of therapy for these diseases was the corticosteroids, which were often less than satisfactory in efficacy and often associated with undesirable side effects, especially in growing children and the elderly. Thus, the search for new agents with different mechanisms of action and which did not have the same adverse event profile as conventional corticosteroids led to the subsequent evaluation of drugs such as tacrolimus and sirolimus to treat several of these diseases. 

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