Evolution of the lymphoid system. I. Evidence for lymphocyte heterogeneity in rainbow trout revealed by the organ distribution of mitogenic responses.

Leukocytes from the various lymphoid tissues of rainbow trout (RBT) were tested for their capacity to respond to the lymphocyte mitogens concanavalin A (Con A), lipopolysaccharide (LPS), and purified protein derivative of tuberculin (PPD). Thymocytes responded to Con A but not to LPS or PPD. In contrast, leukocytes from anterior kidney were stimulated with LPS but not with Con A or PPD. Cells from spleen and peripheral blood were stimulated by each mitogen. However, the degree of stimulation at optimally stimulatory concentrations of each mitogen was distinctive. The finding that the patterns of mitogenic responses of cells from each tissue were significantly different suggested that there is lymphoid heterogeneity in the RBT with a unique tissue distribution. The species source of serum utilized as a medium supplement appeared to be capable of markedly affecting mitogenesis. Thus, LPS and PPD stimulation occurred in medium supplemented with rainbow trout serum (RBTS). On the other hand, LPS and PPD stimulation was not observed in medium supplemented with fetal bovine serum (FBS), with the exception of peripheral blood leukocytes which were stimulated by LPS in culture medium supplemented with FBS. Con A stimulated leukocytes from each lymphoid tissue in medium supplemented with RBTS and, with the exception of cells from anterior kidney, also stimulated cells from each tissue in medium supplemented with FBS. The kinetic profiles of the responses of peripheral blood leukocytes to Con A, LPS, and PPD suggested that the extent as well as the time required for maximal stimulation was dependent on the dose of mitogen.     

Effect of T- and B-lymphocyte mitogens on interactions between lymphocytes and macrophages.

The mitogenic response of murine T cells ² to Con A, S-Con A and PHA was found to be macrophage-dependent. Optimal mitogenic responses were obtained when macrophage-depleted T-cell populations were reconstituted with 5% normal peritoneal macro-phages. Studies were carried out to investigate the effect of T- and B-cell mitogens on in vitro physical interactions between murine lymphocytes and macrophages. This was done by determining the number of T- or B cells binding to macrophages in the absence and in the presence of T- and B cell mitogens, and comparing the results of these experiments with the induction of lymphocyte proliferation. Con A increased the binding of T cells to macrophages when used in mitogenic doses (1–5 μg/ml). Dose response experiments showed that the same dose of Con A which produced maximal mitogenic stimulation also induced the greatest number of T cells to bind to macrophages. Nonmitogenic doses of Con A (20–50 μg/ml) did not enhance the binding of T cells, while identical doses of S-Con A both induced T cell mitogenesis and increased the number of T cells bound to macrophages. Similar results were obtained with PHA. None of the B-cell mitogens tested (LPS, EPO 127 and LAgl) increased the binding of either T or B cells to macrophages. PWM, which is mitogenic for both T and B cells, increased the binding of T cells to macrophages, but not that of B cells. In brief, the four T-cell mitogens tested (Con A, S-Con A, PHA, and PWM) induced specific physical interactions between T cells and macrophages, while none of the B-cell mitogens had any effect on the physical interactions between either B or T cells and macrophages when used in mitogenic doses.     

Time-dependent inhibition of tuberculin-induced lymphocyte DNA synthesis by a serine protease inhibitor

Diisopropylfluorophosphate (DFP), a group-specific irreversible inhibitor of serine proteases, has been shown to exert time-dependent inhibition of DNA synthesis of lymphocytes stimulated by three different B lymphocyte mitogens: purified protein derivative of tuberculin (PPD), endotoxin protein (EP), and lipopolysaccharide (LPS). The time-dependent inhibition profile found in B lymphocytes is absent in concanavalin A (Con A)-stimulated T lymphocytes. Structural analogs of DFP, which have lost the phosphorylating ability, are not inhibitory. Inhibition of DNA synthesis by DFP is reversible in the first 8 hr of mitogenic stimulation. Maximal and irreversible inhibition by DFP occurs around the 16th hour of stimulation. These data support the postulate that a mitogenesis-linked protease, or proteases, in B lymphocytes is absent in the resting cells but is made available several hours before the initiation of DNA synthesis in the late G1 phase of the cell cycle.     

Modification of immune competence by parasitic infections. I. Responses to mitogens and antigens in mice treated with Trichinella spiralis extract

Spleen cells from mice pretreated with a Trichinella spiralis extract (TsE-mice) showed severe depression of the response to lipopolysaccharide (LPS) and to concanavalin A (Con A), slight depression to phytohemagglutinin (PHA) and normal response to tuberculin purified protein derivative (PPD) as compared to saline-pretreated controls. Mice pretreated with bovine serum albumin (BSA-mice) revealed greatly reduced responses to LPS, somewhat reduced response to Con A, and normal responses to PHA and to PPD. Only TsE-mice showed significant reduction in the number of rosette-forming cells and of direct and indirect plaque-forming cells (DPFC and IPFC). BSA-mice exhibited some reduction of the DPFC only. Direct hemagglutinating (HA) titers were equivalent in the 3 groups after immunization with sheep erythrocytes but facilitated HA titers were depressed in TsE-mice. The total number and the number of viable cells were similar in the spleens of all animals. TsE treatment causes a reduction in the number of T1 lymphocytes and an inhibition of the late differentiation of B cells in the spleen. Suppressor T-cells apparently play a major but not exclusive role in T. spiralis-induced nonspecific immunodepression.     

Specific mitogenic activity of 8-Br-guanosine 3',5'-monophosphate (Br-cyclic GMP) on B lymphocytes.

8-Br-cyclic GMP has been found to be a specific B cell mitogen; it triggers athymic nude mice spleen cells and "B mice" spleen cells, nylon adherent, anti-theta and complement-treated cells to proliferate. It does not stimulate thymocytes or purified T cells. The kinetics of the response to Br-cyclic GMP and LPS are almost identical. The mitogenic effect of LPS and Br-cyclic GMP is additive when the two mitogens are given together to cells. Spleen cells (C3H/HeJ strain) that did not respond to LPS were triggered by Br-cyclic GMP to make DNA. In order to achieve maximal stimulation by Br-cyclic GMP, the drug had to be in contact with the cells for more than 24 hr. Br-cyclic GMP was found to be mitogenic for spleen cells from five different mouse strains, but not for human leukocytes. DB-cyclic AMP was found to inhibit the DNA synthesis of T lymphocytes after they interacted with Con A; DB-cyclic AMP had no effect on the ability of the B lymphocytes to be transformed by LPS. The differential effects of cyclic nucleotides on B vs. T lymphocytes are discussed.     

Phylogeny of lymphocyte heterogeneity. II. Differential effects of temperature on fish T-like and B-like cells.

Lymphocytes from the bluegill, a freshwater fish, were observed to undergo in vitro mitogenic responses to a variety of “classical” mitogens. Using cell fractionation approaches based upon surface markers and in vitro mitogenesis, bluegill lymphocytes could be divided into two populations. One population responded to PHA and Con A but not to LPS, contained surface antigens in common with bluegill brain, and did not form spontaneous rosettes with rabbit erythrocytes. The other population responded to LPS but not to PHA or Con A, did not appear to contain surface antigens in common with brain, and did form rosettes with rabbit erythrocytes. The former population responded to mitogenic stimulation very well at 32 °C, whereas the latter population responded better at 22 than at 32 °C. The pattern of mitogenic responses and brain antigen distribution coupled with the observation that mixed lymphocyte responses were obtained at 32 but not at 22 °C makes it likely that the 32 °C responsive population represents the fish equivalent of T cells. The other population may be B cells. These data suggest that the immunosuppressive effects of low temperatures on cold-blooded animals may be effects on the generation of functional T cells and not on B cells.     

C57BL/10/CR mice: nonresponders to activation by the lipid a moiety of bacterial lipopolysaccharide.

C57BL/10/CR mice do not respond to the lipid A moiety of LPS. This defect was demonstrated in vivo by a decreased production of the acute phase serum amyloid protein SAA. In addition, the defect was demonstrated in vitro by using cultures of spleen cells and peritoneal cells. No mitogenesis of spleen cells or enhanced glucose utilization by either spleen cells or peritoneal cells was observed when the cells were stimulated by lipid A or phenol-extracted Escherichia coli K235 LPS. The response of these mice to PHA, Con A, Poly I:C, 8BrcGMP, and butanol extraced E. coli K235 LPS was normal. Thus, the inability of lipid A to stimulate B lymphocyte mitogenesis and activate peritoneal cells in vitro may correlate with its inability to induce the acute phase SAA in vivo. B10/CR mice represent another strain, similar to the C3H/HeJ, which is nonresponsive to lipid A and should be useful in eludcidating the mechanism by which bacterial LPS activates cells.     

Interferon and the cellular immune response: separation of interferon-producing cells from DNA-synthetic cells

Spleen cells from mice were separated by albumin discontinuous density gradient centrifugation into six fractions. Cells from each fraction were cultured with a variety of general mitogens and a specific antigen PPD. The cultures then were assayed for mitogenesis and interferon production. The fraction of cells producing interferon were found to belong to a different population of cells from those undergoing a DNA synthetic response. Treatment of the interferon-producing fraction of cells with anti-theta serum and complement eliminated the interferon-producing capabilities of the remaining cells after exposure to PHA, Con A, and PPD but not after exposure to PWM. The results suggest at least a two-cell requirement for the production of interferon in response to PHA, Con A or PPD stimulation. They also suggest that the interferon-producing cells do not belong to the thymus-dependent lymphocyte subpopulation.     

In vitro studies of the rabbit immune system. IV. Differential mitogen responses of isolated T and B cells.

The mitogenic responses of separated rabbit lymphocyte populations functionally analogous to mouse T and B cells have been tested in vitro. Purified T cells were prepared by passage over nylon wool (NW) and purified B cells prepared by treatment with antithymocyte serum and complement (ATS + C). ATS + C kills 70% of peripheral blood lymphocytes (PBL's) and 50% of the spleen cells while passage over NW yields 40% of the applied PBL's and 5–23% of the applied spleen cells. NW-purified T cells from the spleen or PBL's respond fully to concanavalin A (Con A) but have a reduced response to phytohemaglutinin (PHA) and little or no response to goat anti-rabbit immunoglobulin (anti-Ig). PBL's that survive ATS + C (B cells) are stimulated by anti-Ig but not by Con A or PHA. B cells purified from spleen do not respond to Con A or PHA but will respond to anti-Ig under appropriate conditions. A full spleen B-cell response to anti-Ig required removal of Ig produced by the cultures that blocked anti-Ig stimulation. It is concluded that, for rabbit lymphocytes, Con A and PHA are primarily T-cell mitogens and that anti-Ig is primarily a B-cell mitogen. However, the mitogen response of unfractionated PBL or spleen cell populations indicates an overlap in reactivity. This could be due to cells sharing T and B properties, alteration of cell populations by the fractionation procedures used, or recruitment of one population in the presence of a mitogenic response of the other population.     

Graft-vs-host reactions (GVHR) across minor murine histocompatibility barriers. I. Impairment of mitogen responses and suppressor phenomena

In our laboratory, we have developed a murine model to examine GVHD across minor histocompatibility antigens. In our model, GVHD is induced by injecting B10.D2 spleen cells into irradiated BALB/c recipients. Seven to 10 days after irradiation and injection of cells, there are significant changes in cell function in the recipient spleens. In the B10.D2----BALB/c (600 rad) model, recipient spleen cells are profoundly unresponsive to Con A and LPS stimulation but show increased B cell activity measured by Staphylococcus aureus protein A plaque-forming activity. Spleen cells from such GVH mice profoundly suppress the mitogenic responses of normal BALB/c or B10.D2 spleen cells to Con A and LPS. The degree of impairment of the mitogenic response and the ability to suppress normal cells is proportional to the dose of cells used to induce GVH reactions. Both the inability to respond to mitogens and the capacity to suppress are also related to the dose of irradiation given to the recipients. In addition, immunosuppression across minor histocompatibility antigens shows an unevenhandedness. If we inject parental B10.D2 or BALB/c cells into F1 recipients (P----F1), there is greater inhibition of mitogenic responses when B10.D2 parental cells are given than when BALB/c cells are given to the irradiated F1 recipients. These experiments show that significant immunosuppression occurs during GVH reactions across minor histocompatibility barriers. The degree of suppression varies according to the dose of cells used to induce GVH, the dose of irradiation to the recipient and the "strength" of the GVH recognition system. Such experiments provide models for GVH disease seen in humans who receive treatment for leukemia or other diseases that involves recipient irradiation and infusion of HLA-identical bone marrow.     

Modulation of lymphocyte functions by group A streptococcal membrane

Protoplast membranes isolated from group A streptococci suppress functions of mouse B cells in vivo and in vitro. Intraperitoneal injection 24 or 72 hr (but not 12 hr) before collection of lymphoid cells results in a selective decrease in the mitogenic response of bone marrow cells to dextran sulfate (DS). The response of bone marrow cells to lipopolysaccharide (LPS), and spleen cells to both DS and LPS, is unaltered. In vitro exposure of lymphocytes to membranes concomitantly with mitogen reduces the response to both DS and LPS, however, the DS response is more susceptible to low doses of membrane. Suppression of the response to DS in vitro is not mediated by cells bearing Thy 1.2 antigen. Neither the phytohemagglutinin (PHA)-responsive cells nor the adherent cells participate in suppression of the LPS response in vitro. In contrast to the suppression of B-cell functions neither the PHA nor concanavalin A (Con A) response of mouse bone marrow, spleen, or thymus cells is altered by streptococcal protoplast membranes injected 24 hr before collection of cells. In vitro exposure of spleen cells to a limited range of concentrations of membrane results in an enhanced proliferative response of spleen cells stimulated by suboptimal doses of PHA. This synergism is not mediated by the adherent cells. Addition of membranes to spleen cell cultures in vitro has no effect upon the response of spleen cells to suboptimal doses of Con A or to optimal doses of either Con A or PHA. Higher concentrations of membranes reduce the proliferative response of both control and mitogen-stimulated cells. This nonselective suppression by high doses of membranes is not due to toxicity. Delayed hypersensitivity to sheep erythrocytes is potentiated by injection of membranes. These studies suggest that streptococcal membranes preferentially suppress the immature B cells and enhance certain T-cell functions.     

Differential effect of vanadate on DNA synthesis induced by mitogens in T and B lymphocytes

Summary The effect of sodium orthovanadate on enhancement of DNA synthesis by T and B cell mitogenic agents was studied using murine thymocytes and splenocytes. Addition of vanadate to thymocyte cultures inhibited the mitogenic response induced by concanavalin A in a dose dependent manner (50% inhibition at 10 M). On the other hand, DNA synthesis induced in thymocytes by pokeweed lectin and periodate treatment essentially was not inhibited at the lower vanadate concentrations that were markedly effective for concanavalin A induced synthesis. In addition, no significant inhibition of mitogenesis of splenic B cells in response to lipopolysaccharide and dextran was detectable at lower vanadate concentrations. In the absence of added mitogens, vanadate was found to be mitogenic for a subpopulation of thymus cells but not for splenocytes or T cell enriched splenocyte populations. These results suggest that vanadate affects the mitogenic responses in lymphocytes and that the interaction of vanadate with T and B cells is different.     

Increased mitogenic reactivity of normal spleen cells to T lectins induced by thymus humoral factor (THF)

When normal spleen cells were incubated for 24 hr in medium containing thymic humoral factor (THF) and then stimulated by phytohemagglutinin (PHA) or concanavalin A (Con A), a significant increase in the mitogenic reactivity of these cells was observed. When stimulation to T lectins was performed simultaneously with THF, a strong inhibition in cell reactivity was found. It seems that these opposite effects of THF on cell reactivity to T lectins are determined by the sequence of events which lead to maturation of lymphoid cells. Thymic humoral factor does not modify the response of cells to B mitogen lipopolysaccharide (LPS), thus suggesting that this maturative effect on lymphoid cells is exerted on T lymphocytes only.     

Lectin-induced actin polymerization in human lymphocytes: A possible signal for mitogenesis

Employing the DNase I inhibition assay, a decrease in G-actin is demonstrated in human mononuclear cells following stimulation with mitogenic lectins concanavalin A (Con A) and phytohemagglutinin (PHA), as well as a nonmitogenic lectin, wheat germ agglutinin (WGA). The decrease in G-actin can be prevented by pretreatment of cells with cytochalasin E, indicating that the decrease is likely due to conversion to F-actin. Thus, the receptor-mediated actin polymerization is common to both the mitogenic as well as the nonmitogenic lectins. The maximal decrease in G-actin with Con A and PHA occurs at the same concentrations of the lectins that give optimal mitogenic responses. It is a distinct possibility that actin polymerization could be one of the signals necessary for the initiation of mitogenesis. The difference between a mitogenic and a nonmitogenic lectin may lie in the fact that a second signal (or signals), derived from macrophages, may not be generated by a nonmitogenic lectin such as WGA.     

The type-specific capsular carbohydrate of Hemophilus influenzae B is a potent mitogen for murine B lymphocytes

In this study we investigated the in vitro mitogenic properties of the capsular carbohydrate of Hemophilus influenzae b, polyribosylribitolphosphate (PRP). PRP was found to be a potent polyclonal activator of murine B lymphocytes. PRP induced normal B cells to undergo blastogenesis, DNA synthesis, and differentiation to IgM and IgG secretion. IgG3 accounted for the majority of the IgG. No PRP-specific antibody was detectable, indicating the polyclonal origin of the secreted immunoglobulin (Ig). T lymphocytes were neither activated by PRP nor required for B cell proliferation or Ig secretion. In addition, T cell-depleted spleen cells also depleted of accessory (A) cells by passage through Sephadex G-10 retained responsiveness to PRP. Trace lipopolysaccharide (LPS) contamination was not responsible for the mitogenic effect, as shown by the ability of C3H/HeJ spleen cells to proliferate in response to PRP and by the failure of polymyxin B to inhibit PRP-induced DNA synthesis. The B cell responses induced by PRP and LPS were similar with respect to T cell and A cell independence, to the magnitude of DNA synthesis, and to Ig secretion and the Ig isotypes expressed. These data, taken with the finding that the combination of optimal doses of PRP and LPS did not give an additive DNA synthetic response, indicate that PRP and LPS were activating similar B cell populations. However, in contrast to LPS, PRP was capable of inducing significant DNA synthesis in cultures containing as few as 1,000 B cells, suggesting that PRP-driven proliferation was less dependent on cellular interactions than the response to LPS. The differential ability of PRP and LPS to stimulate C3H/HeJ B cells and to stimulate B cell proliferation at low density indicates basic differences between these two mitogens in their mechanisms of B cell activation.     

Proliferation of murine thymic lymphocytes in vitro is mediated by the concanavalin A-induced release of a lymphokine (costimulator).

Mitogen-induced proliferation of lymphocytes may in theory result directly from the interaction of mitogen with the cells, or indirectly as a result of the mitogen-stimulated release of lymphokines. In the case of murine thymic lymphocytes exposed to concanavalin A (Con A) in tissue culture, we have determined that mitogenesis depends upon a lymphokine. Interaction of the thymic lymphocytes with lectin is necessary, but not sufficient, for mitogenesis. A lymphokine, or costimulator for mitogenesis, is released by normal spleen or thymus cells during the first 16 hr of their exposure to Con A, and in the presence of a phytomitogen it stimulates thymic mitogenesis. Under conditions of low costimulator levels, no mitogenesis follows the interaction of Con A with cells. The response of adult CBA/J mouse thymocytes to phytohemagglutinin (PHA) is very low, compared to their response to Con A. When costimulator is added to PHA, the cells respond as well as they do to Con A. Costimulator does not act through Con A-binding sites on thymus cells. Its production is dependent on both cells carrying omega surface antigen (T lymphocytes) and adherent cells of the macrophage-monocyte series. The adherent population, but not the T cells, may be heavily irradiated without affecting production of costimulator. Costimulator is not a mitogen on its own.     

Mechanism of histamine-induced inhibition of lymphocyte response to mitogens in mice

Histamine induced, in mice, an inhibition of lymphocyte response to PHA and LPS, at molar concentrations ranging from 10^?3 to 10^?9M. This inhibition occurs as a specific interaction between histamine and T lymphocytes bearing H2-type receptors for this hormone (H + cells) and Ly 2 membrane antigens. Two features of the suppressive activity of this T-cell subpopulation were observed: (i) when histamine is added at the beginning of the culture period with PHA or LPS, it activates the suppressor activity of H + cells which act on the lymphocyte population responding to PHA and LPS; (ii) preincubation of spleen lymphocytes with histamine for 24 hr induces suppressor cells which inhibit the response to PHA, but not to LPS, of syngeneic lymphocytes in a coculture system, and which are radiosensitive. The role of PHA as a second stimulus of histamine-induced suppressor cells, and the relation between these cells and PHA or Con A-induced suppressor cells, are discussed.     

Mitogenic activity of Actinomyces viscosus. I. Effects on murine B and T lymphocytes, and partial characterization.

Actinomyces viscosus homogenate (AVIS) contins substance(s) which cause spleen cells from conventional and germfree mice to undergo increased DNA synthesis. This mitogenic effect is primarily on B cells since spleen cells from nude mice or T-depleted spleen cells from conventional mice respond as strongly as conventional (T + B) spleen cells. Mouse thymocytes do not respond mitogenically to AVIS. It is unlikely that the mitogenic acitivity is due to the presence of LPS, since A. viscosus is Gram-positive and is not known to have an LPS cell wall component. Also, AVIS is not inactivated by polymyxin B, as are some preparations of LPS, and C3H/HeJ mouse splenocytes respond strongly to AVIS but not to LPS. The activity is heat stable, is not lost upon dialysis, and is not affected by lysozyme. Mitogenic activity is partially lost when AVIS is digested with nonspecific bacterial protease or treated with metaperiodate. Sodium hydroxide treatment completely abolishes mitogenic activity. Actinomycotic lesions are characterized by a long-tern inflammatory response involving a dense plasma cell infiltrate. We suggest that B cell mitogens form Actinomyces may play a role in the elicitation of the plasma cell component of these lesions.     

Immunologic properties of bacterial lipopolysaccharide (LPS). IV. Cellular basis of the unresponsiveness of C3H/HeJ mouse spleen cells to LPS-induced mitogenesis.

Lymphoid cells obtained from the C3H/HeJ mouse strain respond abnormally to LPS in vitro, as shown by the fact that they are unable to make a mitogenic response to some LPS preparations and make only a low mitogenic response to other LPS preparations. In contrast, cells from a closely related C3H substrain, the C3H/St, are highly responsive to both types of LPS preparations. Experiments were carried out to determine the cellular basis of these genetically determined LPS response differences. This question was approached by studying the mitogenic response to LPS in cultures containing mixtures of various combinations of B cells, T cells, and macrophages from C3H/HeJ and C3H/St mice. Experiments utilizing an LPS preparation to which the C3H/HeJ is totally unresponsive (negative LPS) revealed, first, that either spleen cells, or partially purified T cells and/or macrophages obtained from C3H/St, could not restore the ability of C3H/HeJ spleen cells to respond to LPS, indicating that the C3H/HeJ is not deficient in an LPS-specific helper cell population which may be required for mitogenesis. Secondly, the addition of either spleen cells or partially purified T cells or macrophages from the C3H/HeJ to spleen cells from the C3H/St did not inhibit the mitogenic response to LPS, suggesting that the presence of suppressor cell activity is also not involved. Experiments analogous to those described, except utilizing another LPS preparation to which the C3H/HeJ is partially responsive (positive LPS), also failed to demonstrate reconstitutive or suppressive effects when C3H/HeJ and C3H/St spleen cells were admixed. The results obtained indicate that the defect in the C3H/HeJ mouse strain that limits its responsiveness to positive LPS and which renders it totally unresponsive to negative LPS appears to be an intrinsic defect in the capacity of B cells to react to the mitogenic stimulus of LPS.     

Suppressor cells present in the spleens of Trypanosoma cruzi-infected mice.

Infection with Trypanosoma cruzi decreases the ability of spleen cells from mice to respond to either T cell, concanavalin A (Con A), or B cell, lipopolysaccharide (LPS), mitogens. The effect of infection on the mitogenic response depends on the elapsed time between the day of infection and the time of mitogen presentation. Responses early in infection are normal, whereas later responses to either mitogen are depressed. Spleen cells from late trypanosome-infected mice inhibit the ability of normal spleen cells to respond to Con A or LPS. The cell in the T. cruzi-infected spleen cells responsible for this effect is nonadherent, sensitive to treatment with anti-mouse thymus serum plus complement, but insensitive to treatment with anti-immunoglobulin plus complement. These data indicate that infection with T. cruzi elicits over time the generation of T cells suppressive to T and B cell mitogenic responses.