Lymphocyte activation. V. Quantitation of the proliferative responses to mitogens using defined T and B cell populations

Although mitogens are frequently used for polyclonal lymphocyte stimulation in both experimental and clinical studies, biological tests of this kind encounter several technical difficulties. The relative importance of some of these were studied by using `calibration curves' for mitogenic stimulation. Thymocytes from cortisone-treated mice (T cells) and spleen cells from T cell-deprived mice (B spleen cells) were mixed in different known proportions and stimulated by Concanavalin A (Con-A), which is a T cell mitogen, or lipopolysaccharide (LPS), which is a mouse B cell mitogen.

We have confirmed earlier observations showing that the amount and specific activity of [³]thymidine have to be adjusted to the culture method used. A linear relationship between the responding cell number and incorporated thymidine was promoted when the extracellular thymidine concentration was constant during the labelling period (16 hr). In our system this could be achieved by adding sufficient amount of thymidine in the form of isotope of relatively low specific activity (50 mCi/mmol). In contrast, when isotope of very high specific activity was used, a low number of responsive cells gave almost `normal' incorporation values.

The validity of the use of mitogens was also tested with the T6 chromosome marker method and cell surface immunoglobulin analysis. It was found that the selective responses of T and B cells to T or B cell specific mitogens were maintained in cultures containing varying numbers of T and B cells. The only indication that B cell activating or `potentiating' factors are released by Con-A-stimulated T lymphocytes was observed in cultures with a high proportion (75%) of `T' cells.

Radio-autographic analysis revealed that under the culture conditions in which the majority of T cells from the spleen were stimulated by Con-A, only 20–30% of B cell population responded to LPS and pokeweed mitogen (PWM).

Lymphocyte activation. IV. The ultrastructural pattern of the response of mouse T and B cells to mitogenic stimulation in vitro

Thymocytes from cortisone-treated mice (`T' cells), `B' spleen cells (B lymphocytes from thymectomized, irradiated, marrow reconstituted mice) and normal spleen (T + B) cells were examined by electron microscopy after 60 hours stimulation by Concanavalin A (a T cell specific mitogen), endotoxin (B cell specific mitogen), and pokeweed mitogen (which stimulates both T and B cells). Stimulation of T cells by Con A or PWM induced the appearance of lymphoblasts (Type I) and only PWM or endotoxin stimulated B cells developed `plasmablast' features (dilated, vesicular rough endoplasmic reticulum; Type II). A few stimulated B cells also had lymphoblast morphology. Large cells from normal (T + B) spleen stimulated by PWM were heterogeneous consisting of 55–60 per cent plasmablasts and 40–45 per cent lymphoblasts. It was concluded that the ultrastructure of stimulated lymphocytes depended on whether T or B cells were stimulated and not primarily on the mitogen used. In general, the response evoked by mitogens paralleled at the ultrastructural level that induced by antigens. It was also found that multivesicular bodies and glycogen particles occurred predominantly in the cytoplasm of stimulated T cells (lymphoblasts).

The auto-immunogenicity of articular cartilage

Rats injected with syngeneic chondrocytes or cartilage shavings develop autoreactivity as assayed by the leucocyte migration inhibition test. It is suggested that chondrocyte specific differentiation antigen(s), normally sequestered from the immune system, once exposed experimentally by enzyme treatment or in some human pathological situations are recognized as foreign immunogens and induce a lymphocyte response.

Antigen-binding thymus-derived lymphocytes. I. Rapid method for isolation of theta-positive antigen-stimulated cells

A rapid method for separating SRBC-stimulated populations of theta (θ)-positive thymus-derived lymphocytes from bone marrow-derived lymphocytes and plaque-forming cells has been developed using cotton wool columns. The column effluent was monitored for plaque-forming and `rosette'-forming cells. Stimulated θ-negative cells were found to adhere preferentially to cotton wool. The total recovery of small lymphocytes was 12±3 per cent and the yield of rosette-forming cells was 5.5±4 per cent of which 85±5 per cent were θ-positive.

Antigen-binding thymus-derived lymphocytes. II. Nature of the immunoglobulin determinants

Thymus-derived `rosette'-forming lymphocytes which have been separated from other SRBC-sensitive cells by means of cotton wool columns were examined for the presence of immunoglobulin. This was carried out by inhibition of rosette formation by anti-immunoglobulin sera. Inhibition was effected by a number of anti-IgM sera shown to contain antibodies with specificities directed towards the `hinge' region of the μ chain. No other heavy chain specific antisera were inhibitory.

The ratio of rosette inhibition by anti-κ and anti-λ light chain sera varied during the course of the response to SRBC, the latter inhibiting by 89 per cent 3 days post-immunization.

Lymphocyte activation. 3. Binding sites for phytomitogens on lymphocyte subpopulations

The presence of binding sites for concanavalin A, phytohaemagglutinin and lentil mitogen on the surface of mouse B and T lymphocytes has been investigated in relation to the previously described mitogenic selectivity of these stimulants for T cells. Purified T or B or mixed T/B suspensions of cells have been analysed both for proportions of cells with affinity for phytomitogens and for the relative density of binding sites. In addition, the specificity of mitogens for simple saccharides has been investigated in relation to binding of the former to T and B cells.

Microscopic agglutination and immunofluorescent studies show that virtually 100% of T and B lymphocytes have binding sites for the three phytomitogens. Quantitative absorption experiments have demonstrated that there is virtually no difference in the relative average density of binding sites on T and B cells.

Immunofluorescent studies with Con-A suggested that binding sites are uniformly present over the entire cell surface. However, when lymphocytes are metabolically active an interesting altered localization of bound Con-A molecules to one pole of the cell takes place.

It is suggested that binding sites for the various phytomitogens are qualitatively and topographically distinct on the cell surface but that with respect to any one mitogen T and B cells have qualitatively and quantitatively similar binding sites.

The relevance of these observations to lymphocyte activation is considered.

Lymphocyte activation. II. discriminating stimulation of lymphocyte subpopulations by phytomitogens and heterologous antilymphocyte sera

The mitogenic selectivity of four phytomitogens, phytohaemagglutinin (PHA), concanavalin (ConA), lentil mitogen (LM) and pokeweed mitogen (PWM), and a series of heterologous antilymphocyte sera (ALS) for mouse T and B lymphocytes has been investigated using thymidine uptake as a measure of proliferative activity.

The results show that PHA, ConA and LM stimulate T but not B cells whereas PWM activates both T and B cells. Of six mitogenically active ALS, five were T cell specific and one B cell specific. Cortisone resistant (T) cells within the thymus showed a much greater response to all mitogens than unselected thymocytes. However, ConA and LM activated a considerable response in the latter population.

Selective activation of T and B cells by aspecific means may be useful both as a clinical tool and as an approach to gaining an understanding of antigen induction of immune responses.

Inhibition of human mixed lymphocyte reaction by antibodies to immunoglobulin light chain determinants

The proliferative response of human blood lymphocytes to homologous cells in vitro (i.e. the mixed lymphocyte reaction) has been used as a model of cell-mediated immune responses to investigate the nature of the antigen receptor site involved in the initiation of these reactions. Pretreatment of lymphocytes with the Fabγ monomer of rabbit antisera to human immunoglobulin light chain determinants effectively suppressed subsequent responsiveness to antigen without impairing lymphocyte viability or response to phytohaemagglutinin. Experiments in which the dose of antigen and the time of addition of antigen relative to antiserum were varied suggested that anti-light chain antibodies compete with antigen for the receptor site. These results are discussed in relation to the problem of the chemical nature of the receptor site for transplantation reactions and delayed hypersensitivity.

Response to phytohaemagglutinin of lymphocytes from mice treated with anti-lymphocyte globulin

Thymus, spleen, lymph node and peripheral blood lymphocytes taken from mice treated with anti-lymphocyte globulin (ALG) showed a greatly diminished response to PHA in vitro. Recovery of circulating lymphocyte levels preceded recovery of responsiveness to PHA. The latter could be prevented by reinjection of ALG or by thymectomy. Grafts were rejected within a period equal to the normal rejection time after PHA responsiveness had recovered to a value of approximately 20 per cent of the normal. Thus the effect of ALG on thymus dependent lymphocytes in mice can be monitored by assessing the PHA sensitivity of peripheral white blood cells.