Leucocyte responses in vitro in health and disease
Several variables associated with (i) the lymphocyte transformation (LT) test, (ii) cell surface markers for identifying T and B lymphocyte subpopulations, and (iii) neutrophil chemotaxis in vitro have been studied in healthy individuals and in patients with suspected immunological abnormalities, usually in association with recurrent infections. In normal individuals, lymphocyte transformation in response to polyclonal mitogens, antigens and allogeneic lymphocytes was measured by incorporation of radio-labelled thymidine into DNA (proliferation). Neutrophil chemotaxis to a standard cvtotaxin (casein) was quantified by measuring distances migrated into micropore filters. Both of these test systems were optimised to allow maximal expression of leucocyte responsiveness to the various stimulants, thereby allowing maximal sensitivity for subsequent detection of abnormal responses associaxed with diseases. Wide ranges of lymphocyte responses to each of the different stimulants were found in normal volunteers. A fixed relationship was observed between the responses to the different polyclonal mitogens [ PHA > ConA > PWM ] in healthy individuals. This may have been a result of different mitogens' capacities to stimulate different sub-populations of lymphocytes. Cell fractionation studies suggested that proliferative responses were attributable only to the T lymphocyte subpopulation. However, none of the responses to any of the stimulants correlated with total T cell proportions in the cultured lymphocyte populations. When normally healthy individuals were exposed to antigens in vivo (by immunization or infection), their lymphocytes' responsiveness to all stimulants was depressed or abolished (similar patterns of lymphocyte responsiveness were found in many of the patients). In addition, normal lymphocytes could be induced to show the same pattern of abnormal responsiveness in LT tests by prior exposure to antigen in vitro. Lymphocyte transformation and delayed cutaneous hypersensitivity (DH) (as correlates of specific cell-mediated immunity) were not closely associated within the patient group in general. In most cases of dissociation, DH was found without LT to specific antigens: in such cases lymphocytes were found to retain antigen-responsiveness in vitro by lymphokine secretion. In a minority of cases, LT was found without DH: in such cases lymphocyte-function-inhibiting serum factors were found- Patients who had recently started treatment with prednisolone showed a profound depression of LT responsiveness. However, those patients on long-term maintenance doses of prednisolone appeared to have recovered their LT responsiveness to all stimulants except ConA, and also showed normal neutrophil chemotactic responses. Abnormal neutrophil chemotaxis was found in one-third of the patients studied, and these also tended to show low lymphocyte transformation. Abnormal neutrophil chemotaxis was net found to be directly associated with other abnormalities of neutrophil function, but patients who showed raised NBT-reduction by their neutrophils showed significantly lower chemotactic responses than patients whose neutrophils had deficient intracellular microbicidal capacity: these two patient groups did not overlap. Some relationship was found between neutrophil chemouactic and microbicidal deficiencies in a case of chronic mucocutaneous candidiasis. The general conclusion from these findings is that in most of the patients studied the expression of abnormalities in these in vitro tests of leucocyte functions was not a result of primary deficiencies in the leucocytes themselves, but may have stemmed from extrinsic factors such as abnormalities of regulation of leucocyte functions. Thus, the abnormalities found are not generally considered indicative of a primary immune deficiency, but rather of some form of active inhibition of the immune system in disease states. The clinical consequences for immunocompetence of immunoregulatory activity in disease requires further investigation of the regulatory activities. Possible mechanisms which could account for the changes which were observed in leucocyte responsiveness In vitro are discussed in relation to present knowledge of the immune system.