Activation of T and B lymphocytes by insoluble phytomitogens

The Sézary syndrome lymphoid cell: abnormal surface properties and mitogen responsiveness

The peripheral blood lymphoid cells of five patients with Sézary syndrome (SS) were examined with respect to their surface membrane characteristics and their response to mitogens. These cells showed markedly defective mitogenic responses to a broad dose range of phytohaemagglutinin (PHA), pokeweed mitogen, concanavalin A, and a rabbit antihuman lymphocyte antiserum (ATS), when compared with normal human lymphocytes. SS lymphoid cells (three patients studied) also displayed diminished or nearly absent capacity to form rosettes with unsensitized sheep erythrocytes (E-rosettes), and lacked surface immunoglobulin determinants. Despite their poor mitogenic response to ATS, they were as susceptible as normal lymphocytes to ATS-induced, complement mediated cytotoxicity. By comparison with lymphocytes from patients with chronic lymphocytic leukaemia, however, SS lymphoid cells showed decreased susceptibility to leukoagglutination by PHA. By way of contrast, three patients with mycosis fungoides having normal-appearing peripheral blood lymphocytes showed normal lymphocyte responses to mitogens, as well as normal proportions of E-rosette forming and surface immunoglobulin-bearing lymphocytes. These studies demonstrate that the SS lymphoid cell may, in some cases, lack surface properties and mitogen response characteristics of both B- and T-lymphocytes.

Mobility of cholera toxin receptors on rat lymphocyte membranes

Fluorescein-labeled cholera toxin binds detectably to 40-60% of rat mesenteric lymph node cells and induces a temperature-dependent redistribution (patch and cap formation) of cell surface toxin receptors. The redistribution is inhibited by several "metabolic," "microtubule," and "microfilament" inhibitors, by concanavalin A, and by anticholera toxin IgG. Various studies indicate that cholera toxin is at least bivalent, and that this property may be related to both the induction of receptor redistribution and to the activation of adenylate cyclase. Membrane components which are probably identical to the sialo-glycolipid, GM1 ganglioside, appear to be mobile in the plane of the membrane. The possible role of toxin multivalency and receptor mobility in the mechanism of toxin action is considered.

Inhibition of lymphocyte mitogenesis by immobilized antigen-antibody complexes

Mouse spleen cells, cultured on surfaces coated with antigen-antibody complexes, are inhibited from responding to the B-cell mitogens, lipopolysaccharide, lipid A, Pneumococcal polysaccharide SIII, and poly I:C. The response to the T-cell mitogen, concanavalin A, is also substantially inhibited by immobilized antigen-antibody complexes, but specific inhibition of the response to phytohemagglutinin is minimal. Control experiments showed that immobilized complexes prepared from IgG F(ab')2 fragments and IgA antibodies (both of which fail to bind to Fc receptors when complexed to antigen) did not show significant inhibitory activity when compared with the inhibition observed with complexes prepared from whole IgG. Suspensions of antigen-antibody complexes prepared from the same antigen and intact IgG antibody did not inhibit mitogenesis. None of the mitogens used could be demonstrated to compete with the binding of aggregated immunoglobulin to the B-cell Fc receptor. It appears that the interaction of Fc receptor-bearing lymphocytes and/or macrophages with immobilized complexes prevents lymphocyte activation by mitogens. It is suggested that the mechanism(s) involved may be relevant to antibody feedback control of the humoral immune response.

Changes in ribosomal RNA processing paths in resting and phytohemagglutinin-stimulated guinea pig lymphocytes

Processing of rRNA was examined in resting and phytohemagglutinin-stimulated guinea pig lymphocytes. Synthesis of 1.7 (28S) and 0.7 (18S) X 10(6) dalton rRNA was more than 4-fold greater in phytohemagglutinin-stimulated than in resting cells. A 5- to 10-fold increase in flux of molecules through a 2.3 X 10(6) dalton RNA occurred without a concurrent change in the flux through a 2.6 X 10(6) dalton fraction in phytohemagglutinin-stimulated cells. In both resting and phytohemagglutinin-stimulated lymphocytes, the 2.3 X 10(6) dalton intermediate equilibrated with [3H]methyl label and pulse-chased prior to the 2.6 X 10(6) dalton RNA. The data indicate at least two processing paths in guinea pig lymphocytes; one proceeds to rRNA via a 2.3 X 10(6) dalton intermediate, and another proceeds via a 2.6 X 10(6) dalton RNA. The increase in rRNA synthesis in phytohemagglutinin-stimulated cells occurs primarily through that path containing the 2.3 X 10(6) dalton intermediate.

Quantitation of T and B lymphocytes and cellular immune function in Hodgkin's disease

Peripheral blood T and B lymphocytes were quantitated in 42 patients with untreated Hodgkin's disease and the results compared with the response to phytohemagglutinin (PHA) stimulation and delayed hypersensitivity skin testing. T lymphocytes were identified by an in vitro cytotoxicity assay employing a specific anti-T-cell serum and by spontaneous rosette formation with sheep erythrocytes (E rosettes). The percentage of T cells in the patients was similar to that of normal subjects as judged by the cytotoxicity assay (65 to 90%). In addition, absolute T-lymphocyte counts were normal in 63% of the patients and were generally reduced only in those with lymphopenia. The percentage of T lymphocytes determined by the E-rosette assay was similar to that determined by the cytotoxicity assay in normal controls, but was significantly lower than that determined by the cytotoxicity assay in the patients. Moreover, the decreased response to PHA stimulation in the patients was directly correlated with the decrease in E-rosette formation. These findings suggest that T lymphocytes in the peripheral blood are not generally diminished in untreated Hodgkin's disease. However, a proportion of these cells exhibits altered surface interactions that may account for some aspects of their impaired immunologic function.

Inhibition by colchicine of the mitogenic stimulation of lymphocytes prior to the S phase

Colchicine, vinblastine, and vincristine inhibit the mitogenic stimulation of lymphocytes by concanavalin A as measured by the incorporation of [3H]thymidine and the appearance of blast cells. The inhibitory effect of colchicine could not be accounted for by diminution in cell viability or by metaphase arrest of mitosis in the stimulated cells. Moreover, the inhibition of [3H]thymidine incorporation was not due to blockage of thymidine transport or inhibition of DNA synthesis inasmuch as addition of colchicine had no effect on cells in the S phase of the cell cycle. The time of inhibition was correlated with the kinetics of cellular commitment to lectin activation and the kinetic data indicated that colchicine blocks stimulation early in the sequence of events following addition of the mitogen. These findings support the hypothesis that cytoplasmic microtubular function plays a role in the commitment of resting cells to undergo mitotic division.

The influence of splenectomy on the invitro lymphocyte response to phytohemagglutinin and pokeweed mitogen in Hodgkin's disease

Using tissue culture techniques, the 14C-thymidine incorporation of peripheral lymphocytes in 17 Hodgkin's patients was tested before and after splenectomy under stimulation with phytohemagglutinin and pokeweed. Incorporation under phytohemagglutinin stimulation about 10 days after splenectomy was not affected in Hodgkin's patients with pathologic Stages I and II, but was significantly (p less than 0.005) increased in those with Stages III and IV. The total PHA stimulation potency, i.e. the product of the lymphocyte count and PHA stimulation, increased slightly in both groups. Incorporation under pokeweed stimulation after splenectomy did not significantly differ from that before the operation in the two groups. Although the number of cases studied is rather small, it is concluded that splenectomy causes no demonstrable untoward effect on the cellular immunologic potency. The immunologic state is more likely to be favorably influenced than unfavorably.

Reduced lymphocyte transformation in early cancer of the breast

The cell mediated immune response has been measured in vitro by lymphocyte transformation in 53 patients with malignant tumours of the breast and an equal number of patients in the same age group operated upon for benign tumours. The response to phytohaemagglutinin (PHA) was reduced in the patients with malignant tumours when the lymphocytes were grown either in the patient's plasma or in autologous plasma. This was observed when the response was measured both by the uptake of radioactive DNA precursor and by autoradiography. Reduced lymphocyte transformation was present even very early in the disease and certainly preoperatively. The reduction appeared to be even more marked in the advanced cases. An interesting finding was that the plasma from cancer patients contained a factor which reduced the PHA transformation of lymphocytes from a healthy donor.

Abrin and hurin: two new lymphocyte mitogens

Two plant proteins, abrin from the seed of Abrus precatorius and hurin from the seed of Hura crepitans, are potent lymphocyte mitogens. The extent of stimulation of BALB/C AND CBA strain mouse spleens by these factors is significantly greater than that attained with PHA or PWM and requires thymus-derived lymphocytes. Abrin has been purified to electrophoretic homogeneity, physically characterized, and may undergo conversion from a toxic to mitogenic form. Hurin is the best mitogen we have tested.

Quantitative precipitin studies on the specificity of an extract from Tridacna maxima (Röding)

Haemolymph from the clam Tridacna maxima precipitated with purified H-blood-group substances, Helix pomatia galactogen, and pneumococcus type XIV polysaccharide. Although gel diffusion, gel electrophoresis, and inhibition experiments indicated that only a single precipitating lectin was present in the haemolymph, quantitative precipitin and haemagglutination results suggested that a second agglutinin with anti-H-like specificity was also present. Evidence obtained from hapten inhibition experiments indicated that the precipitin that reacts with pneumococcus type XIV polysaccharide can be inhibited by a number of simple sugars. Of the compounds tested, 2-acetamido-2-deoxy-D-galactose was the best inhibitor of precipitation with pneumococcus type XIV polysaccharide and of haemagglutination with human erythrocytes, but the inhibition experiments showed that the extract was also markedly inhibited by D-galactosamine hydrochloride, D-galactose, lactose, and p-nitrophenyl beta-D-galactopyranoside. The latter compound was more active than its parent sugar, which was in turn a more potent inhibitor than p-nitrophenyl alpha-D-galactopyranoside. Melibiose, raffinose, and stachyose, compounds which each contain terminal alpha-linked D-galactopyranosyl residues, were relatively weak inhibitors. The combining sites of the lectin that reacts with pneumococcus type XIV polysaccharide appear, therefore, to be most complementary to 2-acetamido-2-deoxy-D-galactopyranosyl residues, probably in beta linkage.

B lymphocyte activation and lattice formation

When B lymphocyte activation is viewed within the general context of the clonal selection theory it is seen that this complex process must, under normal physiological conditions, be initiated only after antigen recognition by the B cell, that is, after antigen binding to the cells immunoglobulin receptors. The cross linking of receptors by effectively multivalent antigens, so as to form a receptor-antigen lattice may be generally required for activation. A theory is developed for the rate of lattice formation in the presence of inhibition by free hapten. It is shown that free hapten can very effectively inhibit the rate of lattice formation, particularly on high affinity cells, even though it cannot compete with multivalent binding at equilibrium.

The immunological properties of haptens coupled to thymus-independent carrier molecules. III. The role of the immunogenicity and mitogenicity of the carrier in the induction of primary IgM anti-hapten responses

Hapten (DNP-lys) conjugates of two putatively nonimmunogenic polymers, hyalutonic acid and poly-gamma-D-glutamic acid, induce significant primary IgM anti-DNP responses in C3H mice. Preparations of various immunogenic (Type 3 pneumococcal polysaccharide (SIII), levan, E. coli lipopolysaccharide) and nonimmunogenic (hyaluronic acid and poly-glutamic acid) polymers were tested for their ability to act as polyclonal mitogens in vitro. In serum-containing spleen cell cultures, only lipopolysaccharide stimulated substantial cell proliferation. In serum-free medium, and using high specific activity [3H]thymidine, lipopolysaccharide, levan, SIII and to a lesser degree hyaluronic acid induced significant thymidine incorporation. However, under the latter conditions cell survival and proliferation were much less impressive. There was no apparent correlation between the capacity of various polymers to induce lymphocyte proliferation and their "potency" as carriers for the generation of a primary IgM anti-DNP response. Furthermore while low doses of lipopolysaccharide elicited "polyclonal" antibody formation in vivo, high doses of SIII, levan and hyaluronic acid did not. These results indicate that T cell-independent B cell triggering is dependent on the polymeric nature of the antigen, and that polymers need not be immunogenic or mitogenic to act as carriers for the induction of primary IgM anti-hapten antibody responses.

Stable alterations at the cell membrane of Chinese hamster ovary cells resistant to the cytotoxicity of phytohemagglutinin

Chinese hamster ovary (CHO) cells selected for resistance to the cytotoxicity of phytohemagglutin (PHA) have been found to exhibit stable alterations at their plasma membranes. The PHA-resistant (PhaR) cells bind markedly less 125I-PHA than do sensitive CHO cells and also exhibit an increased sensitivity to the cytotoxicity of concanavalin A, a lectin of different receptor specificity. Mutagenesis with ethylmethanesulfonate increases the proportion of PhaR cells 20- to 100-fold. PHA-resistant cells maintained for up to 8 months in continuous culture in the absence of the selective agent have retained the PhaR phenotype. These and other characteristics of the experimental system suggest that CHO cells selected for PHA resistance are authentic somatic cell mutants. The Pha marker appears to behave recessively in hybrids formed between PhaR and PhaS cells.

Concanavalin A as a probe for studying the mechanism of metabolic stimulation of leukocytes

The disruption of the molecular organization of the plasma membrane of leukocytes by phagocytosable particles, or by agents such as surfactants, antibodies, phospholipase C, fatty acids and chemotactic factors, leads to a stimulation of the phagocyte oxidative metabolism. Concanavalin A (Con A) has been used as a tool to study the mechanism of this metabolic regulation. The binding of Con A to the surface of polymorphonuclear leukocytes (PMNL) or macrophages produces a rapid enhancement of oxygen uptake and glucose oxidation through the hexose monophosphate pathway (HMP). This is explained by an activation of the granular NADPH oxidase, the key enzyme in the metabolic stimulation. The effect of Con A is not due to endocytosed lectin, since Con A covalently coupled to large sepharose beads still acts as stimulant. The metabolic changes caused by Con A are reversible. If, after the onset of stimulation, sugars with high affinity for Con A are added to the leukocyte suspension, the activity of granular NADPH oxidase and the rate of respiration and glucose oxidation return to their resting values. The metabolic burst, while partially supressed by treatment of PMNL with iodoacetate, sodium flouride and cytochalasin B, is slightly increased by colchicine. Con A induces a selective release of granular enzymes (beta-glucuronidase, peroxidase, alkaline phosphatase) from PMNL, whereas no leakage of cytoplasmic enzymes is observed. The enzyme release is inhibited by iodoacetate and by drugs known to increase cell levels of cyclic AMP. Based on a current view of the mode of interaction between Con A and cell surfaces, a model of the metabolic disruption of leukocytes is presented.

Selective triggering of human T and B lymphocytes in vitro by polyclonal mitogens

Human lymphocytes from spleen and tonsils have been cultured with a variety of polyclonal mitogens. Cultures consisted of either unseparated T and B cells or alternatively purified T or B lymphocytes. The purity of the starting cell populations and the origin of activated lymphoblasts was analyzed with a panel of seven markers which discriminate between T and B cells. The selectivity of the lymphocyte responses was influenced by cell populations in a given culture, the mitogen used, and to a limited extent on culture conditions. Purified T lymphocytes from tonsil and spleen responded to phytohemagglutinin (PHA), pokeweed mitogen (PWM), and staphylococcal enterotoxin B (SEB). Purified B cells from spleen responded well to PWM, weakly to SEB and lipopolysaccharide, but not at all to PHA. Tonsil B cells responded weakly to PWM and SEB but not to PHA. Some B lymphocytes do respond to PHA in the presence of activated T cells. These results are discussed in relation to previously reported selective responses of human cells and parallel studies in animal species.

Cellular interactions in the proliferative response of human T and B lymphocytes to phytomitogens and allogeneic lymphocytes

In vitro studies were performed to determine the proliferative responsiveness of human peripheral blood thymus-dependent (T) and thymus-independent (B) lymphocytes to phytomitogens and allogeneic lymphocytes. Recombination of T and B cells, with selective inhibition of proliferation of one of the two populations, was used to identify cellular interactions which may contribute to cell proliferation. The distinctive feature of human T lymphocytes to form rosettes with unsensitized sheep erythrocytes was utilized to separate human peripheral blood lymphocytes into highly purified resetting (T) and non-rosetting (B) cells. The proliferative response of these separated lymphocyte subpopulations to various stimulants was assessed from the uptake of tritiated thymidine into DNA. Phytohemagglutinin, concanavalin A, pokeweed mitogen, and allogeneic lymphocytes stimulated separated T cells, whereas no proliferation was observed with the T-cell-depleted B-cell population. This suggests that it is the human T cell which is activated directly by these stimulants. In the presence of T cells (proliferating or nonproliferating), B cells were capable of proliferation following stimulation with phytomitogens, but not in response to histocompatibility antigens. Thus, T-cell-mediated B-cell proliferation contributes to the overall lymphocyte response in phytomitogen-stimulated T + B cell mixtures, but not in human mixed leukocyte cultures. T-cell activation by allogeneic cells required the presence of monocytes; in contrast, the three tested phytomitogens stimulated T cells in the absence of monocytes. This indicates that direct interaction of mitogens with lymphocyte membrane receptors is sufficient to trigger T cells into proliferative response. However, monocytes considerably enhanced the proliferative response of T cells in a dose-dependent fashion; this monocyte-dependent mechanism of T-cell activation was predominant at lower concentrations of phytomitogens, and contributed relatively less at higher mitogen doses. Both, the direct, monocyte-independent, and the indirect, monocyte-dependent T-lymphocyte activation contribute to the total in vitro response of lymphocyte preparations to phytomitogens.