Specific antibody responses to influenza virus were obtained in vitro from human blood mononuclear cells (PBM). The response was T cell-dependent, as shown by separation of PBM into E rosette-positive (E+) and -negative (E-) populations. The histocompatibility requirements for T-B cells interactions in this response were analyzed by recombining E- and E+ fractions from donors with varying degrees of HLA compatibility. No antibody formation was obtained from any allogeneic combination except for the special case of HLA identical siblings. As these experiments included combinations with shared or identical HLA-DR specificities, it was unlikely that genetic restriction alone could account for the failure of T-B cell collaboration. Evidence that suppression was responsible for the lack of antibody formation was obtained from experiments in which allogeneic E+ cells profoundly depressed specific antibody responses of intact PBM. In contrast, no such suppression was seen in pokeweed mitogen-driven polyclonal Ig synthesis for which there are no major histocompatibility complex requirements for T cell help. The suppressor activity of allogeneic E+ cells was found to be radiation-sensitive. By irradiating E+ cells, it was, therefore, possible to test for T cell help across an HLA barrier without unwanted suppressor effects. Under these conditions, (irradiated) E+ cells were able to collaborate with allogeneic E- cells even with no HLA alleles in common. This was true even when autologous monocytes were depleted from the helper E+ population. Supernatants collected from antigen-driven cultures of allogeneic E- and E+ cells were able to replace helper T cells in the specific antibody response to influenza virus. The apparent lack of genetic restriction in these responses might, therefore, be explained by the production of a nonrestricted helper factor.

Histocompatibility requirements for T cell help in specific in vitro antibody responses to influenza virus by human blood lymphocytes

Antigen-specific suppressor factors are products of suppressor T cells which possess specificity for the antigens by which they are induced. They probably play a significant role in immunoregulation. They are not classic immunoglobulins, and they carry determinants of the major histocompatibility complex. This review discusses the literature on their production, structure, genetic restriction in activity and mechanism of action.

Antigen-specific T-cell factors.

The study of human B lymphocyte activation has been the object of increasing interest over the last 5 years. As more information was being gathered on the requirements for and the regulation ofB ce]I activation in experimental animals, it became imperative to determine whether the same principles apply to human B cell activation. Such information would be necessary to define the physiology of immunoglobulin production as well as of specific antibody production in health and disease. The present review intends to summarize some aspects of the current information on human B cell activation and draws heavily on the results of work performed in the author's laboratory. The subject is divided into five parts: 1) Maturation stages of human B cells 2) Methods of measurement of human B cell activation in vitro 3) Activation of human B cells by polyclonal activators (PBA) 4) Activation of human B cells by antigen-specific factors 5) Regulation of human B cell activation in vitro.

Regulation of human B cell activation.

Based on methods used for the in vitro induction of antigen-specific suppressor cells in the mouse, we have cultured Ficoll-Isopaque-separated human blood cells with high dose of antigen (100 microgram/ml) in Marbrook culture vessels for 4 days. The resulting cells, when further recultured for 24 hr with a low dose of antigen (1 microgram/ml), released into the supernatant material, termed 'suppressor factor', which inhibited, in an antigen-specific manner, the antibody response of mouse spleen cells in culture. The suppressor factor was analysed using immunoabsorbents, and was bound to and eluted from specific antigen, concanavalin A and lentil lectin, anti-human Ia antibodies, and anti-mouse suppressor factor antibodies, but was not bound to antibodies against human IgG.

Induction of human antigen-specific suppressor factors in vitro.

The lifting of a corner of the veil which covers the regulation of human antibody synthesis has lead to an increasing challenge to investigate the underlying mechanisms. Studies on the stimulation by mitogens of immunoglobulin synthesis in human lymphocytes in vitro were published in 1971 by Cooper and Lawton [15]. Over the last three years these methods have been further developed allowing the antigen-induced antibody response to be studied [-20]. Although it has been known that T cells can either diminish or augment the immune response, this knowledge has only recently passed from a concept to a distinct entity. Following the discovery of separate subsets of human T lymphocytes one could then study the basis underlying the regulatory processes. When techniques for isolation of these subsets became available, it then became apparent that the magnitude of an antibody response in vitro reflects the net result of the activity of multiple sets of interacting lymphocytes. Thus the concept of a two-cell (T-B)-interaction appears to be an oversimplification. As in vivo manipulations are often impossible, investigations on the human immune response are more limited than analogous studies in mice. However, the results of many experiments aimed at elucidating these various regulatory mechanisms in man, have been published over the past few years. Some exciting new developments in this area will be discussed in this contribution. Our selection can, of course, be subject to comment. It is based, however, on data which may be relevant for a better understanding of certain immune disorders in clinical medicine and which will illustrate the complexity of the mechanisms of communication between lymphocytes.

In vitro antibody response of human lymphocytes.

The interaction of Tand B-cells in thymus-dependent antibody responses has been the subject of much investigation, but the mechanism is still poorly understood. It has been shown by several investigators l-; that this interaction does not necessarily require cell-cell contact but can be mediated by soluble factors. Two distinct types of helper factors have been described, those that are antigen-specific M and those that are 7

Human t-cell responses in vitro: cell interactions and factors

Chapter 13 – human antigen specific helper t cell factors in b cell responses

Genetic control of T cell-macrophage interaction in helper cell induction in vitro.

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Human t-cell responses in vitro: cell interactions and factors

Chapter 13 – human antigen specific helper t cell factors in b cell responses

Genetic control of T cell-macrophage interaction in helper cell induction in vitro.