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In vitro lymphocyte responses with particular reference to tuberculous infections Clements, Donna Valerie Margaret

Abstract

Active tuberculosis is a frequent complication of Hodgkin's disease and it has been demonstrated recently that the circulating lymphocytes are abnormal in this disease (48). Furthermore, reactivation of tuberculosis following steroid therapy is a common complication (56) and it is now well established that steroids are toxic to lymphocytes (57). With this background evidence to suggest the importance of normal lymphocyte function in host resistance and the accidental finding of a poor lymphocyte response in a tuberculous patient, a study of the in vitro reaction of the lymphocytes in tuberculous patients was undertaken. In vitro cultures of peripheral white blood cells will undergo transformation and mitosis when in the presence of phytohemagglutinin (PHA), an extract of the red kidney bean Phaseolus vulgaris. The number of cells which transform or enter mitosis in the culture is representative of the individual's immune responsiveness. In the tuberculous patients studied, irrespective of the state of their disease, the mean mitotic index (the number of cells in mitosis per thousand cells) was found to be significantly lower than normal controls suggesting that their mean immunological capacity is below normal. During the course of the tuberculous study one of the individuals used as a normal control came down with the "flu" on the evening of the day her blood was taken. The PHA mitotic index was found to be severely depressed. To study the effect of such acute upper respiratory infections, presumably of viral origin, mitotic indices were determined on blood samples taken from laboratory volunteers who felt they were coming down with a cold. The indices were found to be depressed in all cases as compared to healthy normals. The reaction of delayed hypersensitivity and the relationship of this reaction to immunity and tuberculosis has been a matter of study for many years. It seems clear that the individuals in the population that later develop tuberculosis are drawn largely from those members who have a positive skin test while those with a negative skin test have been found unlikely to develop tuberculosis to the point of not being required to have X-rays in many instances. Tuberculin PPD (purified protein derivative) was one of the first antigens shown to be capable of transforming lymphocytes in vitro (60, 61) providing the individual had had prior sensitization. As all tuberculin negative student nurses entering training at the Vancouver General Hospital receive a bacillus Calmette Guerin vaccination (BCG), they were chosen for study in order to elucidate the relationship of in vivo and in vitro responses to the tubercle antigen, PPD. As the number of cells responding to PPD is much less than responding to PHA, the mitotic index is a very insensitive method to use in determination of in vitro responsiveness to antigen. Therefore, the response in vitro was determined by the incorporation of (3)H-thymidine into DNA of stimulated lymphocytes. It was found that in 12 to 18 months after vaccination with BCG nurses who had become skin test negative to PPD did not differ significantly in their in vitro response from nurses who had remained skin test positive. A correlation was found between the PHA and PPD in vitro responses which suggests that the response to the general stimulus, PHA, is an indicator of the reaction that can be mobilized to specific antigen. Varying the dose of BCG that was administered affected only in vivo responses. Finally, contrary to many reports, no quantitative correlation was found between in vivo and in vitro responses to PPD following BCG vaccination.

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