Patients with sarcoidosis display a mixture of depressed cell-mediated immunity and increased humoral system activity. The absolute number of circulating T lymphocytes is usually decreased. Levels of B lymphocytes may be normal or increased. The presence of increased T cells in the granulomas indicate that these are T-lymphocyte related granulomas. Measurement of the macrophage migration inhibition factor in patients wit sarcoidosis is further evidence of the presence of increased numbers of activated lymphocytes.
Patients are usually anergic to skin test antigens.
This deficiency of delayed hypersensitivity is persistent and often does not change when patients improve clinically. It has been assumed that replacement of lymph node tissue by sarcoid granulomas produces the lymphopenia and immune anergy dependent upon lymphocyte. Serum immunoglobulin levels may be normal but IgG is elevated in about half the patients. The humoral antibody response is not impaired and patients have no increased predisposition to infection as a result of T cell abnormalities. Serum complement, reflecting an acute phase reaction, may be increased in active sarcoidosis but are generally normal in subacute and chronic cases.