Histamine synthesis by mouse T lymphocytes through induced histidine decarboxylase.

When spleen cells of C57BL/6 mice or mast cell-deficient W/Wv mice were cultured, their histidine decarboxylase (HDC) activity increased with increases in the histamine concentration in the cells and the medium. Addition of concanavalin A (Con A) or Escherichia coli lipopolysaccharide (LPS) enhanced the increase. The removal of adherent cells reduced both the control HDC activity and the response to the mitogens. Purified T lymphocytes responded to Con A but not to LPS. Neither Con A nor LPS had any effect on B lymphocytes. Treatment of T cells with anti-Thy-1.2 and complement completely abrogated the induction of HDC. Histamine synthesis dependent on Con A by T cells was stimulated by the addition of conditioned medium from peritoneal adherent cells activated with LPS. The addition of recombinant interleukin-1 (rIL-1) or peritoneal adherent cells fixed with paraformaldehyde significantly enhanced HDC induction dependent on Con A in T cells. These results suggest that histamine is synthesized by T lymphocytes through HDC and that the reaction was enhanced by a soluble factor(s) released from macrophages.     

Isoprinosine restores in vitro T lymphocyte functions of cyclophosphamide immunosuppressed mice

The effect and the mechanism of action of isoprinosine has been investigated in several models of in vitro activation of lymphocytes. Isoprinosine added to spleen cell cultures enhanced lymphocyte proliferation induced by concanavalin A or allogeneic stimulation as well as the generation of allospecific cytotoxic T cells. The effect of isoprinosine on T lymphocyte proliferation in vitro was specially marked when mice were treated with cyclophosphamide (75-200 mg/kg) 16-24 h before the onset of cultures. No effect was observed on B cell proliferation to LPS. Addition of inosine or adenosine also enhanced proliferation of cells from both normal and cyclophosphamide treated mice. Isoprinosine and inosine and, more markedly, adenosine, augmented interleukin-2 activity in concanavalin A supernatants of spleen cells from the same animals.     

Primary in vitro plaque-forming cell response to DAGG-Ficoll: LPS-induced enhancement mediated by interleukin-1.

The specific primary in vitro plaque-forming cell (PFC) response of C57B1/6 nu/nu spleen cells to the Type 2 T-independent (TI-2) antigen DAGG-Ficoll was analysed in the absence of T cell help in a serum-free medium. Lipopolysaccharide (LPS) enhancement of the antigen-specific response was shown to be mediated by soluble factors contained in the supernatants of LPS-induced bone marrow-derived macrophages. The activity of these supernatants was not associated with residual LPS, since the antigen-specific response of B cells from mice genetically deficient in LPS receptors was equally well enhanced. The activity of these supernatants was associated with interleukin-1 (IL-1) and partially purified IL-1 prepared from P388D1 cells also enhanced the primary in vitro response to DAGG-Ficoll. Limiting dilution analysis experiments showed that only in the presence of exogenously added IL-1 could a single cell type, presumably the B cells, be shown to be limiting.     

犬蛔虫（Toxocaracanis）对感染鼠的细胞免疫和IL－1、IL－2免疫调节作用的影响

应用犬蛔虫（Ｔ．ｃａｒｎｉｓ）的感染性虫卵口饲感染Ｃ３Ｈ／ＨｅＮ鼠，体外培养后观察脾细胞的免疫学变化。感染第１－４周的脾细胞用ＣｏｎＡ刺激，Ｔ细胞的增殖反应，ＩＬ－２的诱生均明显地受到抑制，而且感染鼠脾细胞抑制了正常鼠脾细胞对ＣｏｎＡ的反应。感染鼠的脾细胞经ＳｅｐｈａｄｅｘＧ－１０过柱后，Ｔ细胞则不显示被抑制作用。表明影响Ｔ细胞被抑制作用的是感染鼠的巨噬细胞。相反，感染第１－４周的鼠所产生的ＩｇＧ和ＩｇＭ等抗体的Ｂ细胞活性增强；用ＬＰＳ刺激巨噬细胞诱生的白介素（ＩＬ）ＩＬ－１也增多。     

Studies of the immunological activities of the outer membrane protein from Escherichia coli

The outer membrane protein (OMP) prepared from Escherichia coli was found to be a potent mitogen for murine B cells and to be capable of inducing polyclonal antibody formation as well as a proliferative response. Spleen cells from nude mice responded equally as well to OMP as those from their normal litter-mates, whereas nylon-wool-purified T cells or thymocytes failed to respond. The proliferative response was dependent on the presence of macrophages. The macrophage dependency of the polyclonal antibody response seemed to be less than that of the proliferation. OMP was mitogenic for lipopolysaccharide (LPS)-resistant C3H/HeJ spleen cells, further indicating that OMP is an unique B-cell mitogen distinct from LPS.

OMP also enhanced the specific antibody response sixty-seven-fold to an optimal dose of sheep red blood cells (SRBC) in vitro. The kinetics of the response, however, was not altered from that of cultures without OMP. The anti-SRBC response of spleen cells from C3H/HeJ mice was also enhanced by the addition of OMP, suggesting that the adjuvant effects were not due to the LPS in the preparation. Antibody responses in vitro to TI-1 antigens, trinitrophenyl-LPS (Boivin) (TNP-LPS^B) and TNP-Brucella abortus, were not enhanced in the presence of OMP. In contrast OMP enhanced the response to TI-2 antigens, TNP-LPS^W (Westphal) and dinitrophenyl-Ficoll and T cells were shown to be required for these augmented antibody responses. Enhancement was not seen in nude mouse spleen cell cultures but was seen when nylon-wool-purified T cells were added to the cultures.

     

B cell-mediated down-regulation of IFN-gamma and IL-12 production induced during anti-tumor immune responses in the tumor-bearing state

Unfractionated spleen cells taken from tumor-bearing mice contained tumor-primed T cells which produced lymphokines such as IFN-gamma and IL-2 through collaboration with antigen-presenting cells (APC) binding tumor antigens when cultured in vitro. Here, we investigated the regulatory mechanisms underlying IFN-gamma production by T-APC interactions. Elimination of B cells from a splenic population of tumor- bearing mice resulted in enhanced IFN-gamma production. Adding B cells back into cultures down-regulated IFN-gamma production to almost the same levels as those induced by unfractionated spleen cells. IL-2 production was not enhanced by B cell depletion, but rather was significantly suppressed. IFN-gamma-selective up-regulation was due to an enhancement of IL-12 production because IL-12 was detected in B cell- depleted cultures and enhanced IFN-gamma production was prevented by addition of anti-IL-12 mAb or anti-CD40 ligand (CD40L) mAb capable of inhibiting CD40L-induced IL-12 production. These results indicate that B cells interfere with IFN-gamma production induced through interactions between anti-tumor T cells and APC, and this suppressive effect is based on the capacity of CD40+ B cells to down-regulate the CD40L-induced IL-12 production by APC.      

Restoration of impaired immune functions in aging animals. VI. Differential potentiating effect of 2-mercaptoethanol on young and old murine spleen cells

The differential effect of 2-mercaptoethanol (2-ME) on spleen and bone marrow cells of young and old mice was determined in vitro. Both the ability of spleen cells to proliferate and to generate Ig-secreting cells and the capacity of bone marrow cells to generate myeloid colonies were assessed. All three activities assessed in both young and old mice were enhanced by the presence of 2-ME, but a differential effect with respect to age was noted in only one. This was the polyclonal activating antibody response to bacterial lipopolysaccharide (LPS) in which 2-ME enhanced young spleen cells to a greater extent than old spleen cells, although their mitogenic responses to LPS were enhanced to the same extent. The ability of 2-ME to enhance old spleen B cells to proliferate but not differentiate in their response to LPS would suggest that aging alters certain subpopulations of spleen cells, some of which are sensitive and others insensitive to the potentiation effects of 2-ME. The enhancing action of 2-ME on the proliferative activity of LPS-stimulated young spleen cells was reduced drastically by decreasing the number of T cells by prior treatment of spleen cells with anti-T cell reagent. The proliferative activity was then brought back to normal pretreatment level by adding enriched T cells. Therefore it would appear that regulatory T cells are the target of the enhancing action of 2-ME. The failure of old spleen cells to respond vigorously to the polyclonal activating action of LPS and 2-ME individually and in combination would indicate that age-related alterations may be taking place in the B cells and/or the regulatory cells. Young-old spleen cell mixture study indicates that there are regulatory cells in old spleen cells which can inhibit B cell differentiation but not B cell proliferation.     

Auto-MHC class II-reactive T cell line obtained from MRL/+ mice suffering from lpr-GVHD. II. Analyses of functional characteristics of T cell line by in vivo administration.

Functional characteristics of an autoreactive (I-Ek-restricted) T cell line (l/+ T1), previously established from MRL/M(p-)+/+(MRL/+) mice with lpr-GVHD, were analyzed in vivo. Intravenous injection of l/+ T1 cells to non-irradiated H-2k (MRL/+ or AKR) mice (but not H-2d mice) induced enhanced spontaneous proliferation of recipient spleen cells; this was also I-Ek self-restricted. This augmented self-reactivity seemed to be mediated by recipient L3T4+ T cells, since few l/+ T1 cells were detected in the spleen cells of l/+ T1-injected AKR mice by cell surface marker analyses, and the treatment of the spleen cells with anti-Thy-1.1 antibody (Ab) or anti-L3T4 Ab plus complement abolished this enhanced spontaneous proliferation. The production of IgM rheumatoid factor (RF) in AKR mice and IgG RF in MRL/+ mice increased, although no enhancement of anti-ssDNA Ab production was observed. Judging from both spleen B cell proportion and serum Ig levels, autoantibody induction by the injection of l/+ T1 cells was not associated with polyclonal B cell activation. When lethally irradiated B10 congenic mice were used as recipients, B10. BR mice showed elevated levels of IgM anti-ssDNA and IgM RF 1 wk after l/+ T1 cell injection; it is likely that lethal irradiation causes autoantigens, particularly DNA, to be exposed. These findings suggest that the autoreactivity of l/+ T1 cells can be transferred to recipient L3T4+ T cells via T-T interaction or the immunological network, and that increased autoreactivity induces autoantibody production in the presence of autoantigen stimulation. In contrast to the stimulatory effects observed in AKR and MRL/+ mice, MRL/Mp-lpr/lpr(MRL/lpr) mice showed a different response to the injection of l/+ T1 cells; spontaneous proliferation of spleen cells and autoantibody production were not enhanced, and suppression of the mitogen responses was observed. It is discussed that lpr-GVHD may be due to these unusual features of MRL/lpr mice.     

Macrophages Suppress Direct B-Cell Activation by Lipopolysaccharide

The influence of macrophages on polyclonal B-cell responses to lipopolysaccharide (LPS) and on a primary, specific immune response to a hapten-LPS conjugate was studied in mouse spleen and lymph node cells in serum-free and serum-supplemented cultures. Macrophages were found not to be necessary, and B cells were directly activated by LPS. In serum-free cultures of macrophage depleted spleen cells, (a) proliferation and antibody secretion occurred at normal levels or were enhanced when compared with normal spleen cells, (b) the responsiveness of limiting cell numbers to LPS was better than in normal spleen cell cultures, (c) LPS did not increase the number or activate residual macrophages, (d) the primary specific response to a hapten-LPS conjugate developed normally, (e) peripheral lymph node cells, which are known to contain a very low concentration of macrophages, from normal or congenitally athymic (nude) mice mounted excellent proliferative responses to LPS Furthermore, in cultures supplemented with fetal bovine serum, depletion of adherent cells resulted in enhancement of LPS-induced B-cell responses. Addition of peritoneal macrophages to adherent cell-depleted spleen cells produced suppression at all concentrations of both mitogen and adherent cells. Suppressive activity could also be demonstrated in supematants from adherent cell cultures stimulated by LPS     

Effects of Carbon Dust Inhalation on the Cell-Mediated Immune Response in Mice

The effects of carbon dust inhalation on the bone marrow-derived (B) and thymus-derived (T) lymphocyte populations of spleen and mediastinal lymph node (MLN) cultures were examined. The concanavalin A (Con A)-responsive cell population (T cells) in the spleen was found to be depressed after 7 days of pre-exposure to carbon dust. However, this effect was transient, and after 14, 21, and 28 days of pre-exposure to carbon dust, the Con A-responsive cells exhibited a 30 to 40% enhancement over control group responses. Conversely, Con A-responsive cells in the pooled MLN cultures exhibited depression, ranging from 22 to 33% below control group values, after 7, 14, and 28 days of pre-exposure to carbon dust. The lipopolysaccharide (LPS)-responsive cell population (B cells) in the spleens of carbon-exposed mice was found not to differ significantly from control group values after all times of pre-exposure. LPS-responsive cells in the MLN cultures exhibited enhancement, ranging from 49 to 74% above control values, after 14, 21, and 28 days of pre-exposure to carbon dust. The ability of carbon spleen cell cultures from carbon-exposed mice to undergo antigen induced blast transformation after sensitization with Mycobacterium tuberculosis H37Ra was also determined. Mice exposed to carbon dust inhalation 2 weeks before and 3 weeks after aerosol or subcutaneous immunization exhibited significantly enhanced ratios of transformation upon culture of their spleen lymphocytes with purified protein derivative of tuberculin.     

Histamine synthesis by non-mast cells through mitogen-dependent induction of histidine decarboxylase.

Culture of spleen cells of C57BL/6 mice led to a spontaneous increase in activity of histidine decarboxylase (HDC) in the cell and the medium. Concomitantly histamine increased in the cells and, especially, in the medium. Addition of concanavalin A (Con A) or lipopolysaccharide (LPS) to the culture enhanced these processes. There was also a significant Con A-dependent increase in HDC activity and histamine biosynthesis in the culture of spleen cells of genetically mast-cell deficient W/Wv mice. Peritoneal macrophages of C57BL/6J mice had constitutively 11-19-fold as much HDC as T and B lymphocytes when compared on the basis of same number of cells. Con A had no effect on HDC activity when the macrophages were cultured alone. However, co-culture with T lymphocytes, separated from macrophages by a millipore filter membrane (pore size, 0.45 micron), rendered the macrophages responsive to Con A, leading to a notable increase in HDC activity in the cell. Addition of LPS caused a small but significant increase in HDC activity in macrophages, even when the cells were cultured alone. Co-culture with T or B cells enhanced the LPS-dependent increase in HDC activity in macrophages. In contrast, the HDC activity in T and B lymphocytes did not change essentially in the presence of any of these mitogens, even when they were co-cultured with macrophages. These results suggest that histamine is synthesized by non-mast cells through HDC.     

Roles of IL-2 and antigen in the later stages of the primary antibody response.

Spleen cells, obtained 2-5 days after in vivo priming with sheep erythrocytes (SRBC), were cultured to determine the presence of plaque-forming cell (PFC) precursors capable of developing into mature PFC under the influence of various stimulants. Lipopolysaccharide (LPS), added together with SRBC at the initiation of a 48-hr in vitro culture, enhanced the PFC response of primed spleen cells. In vivo priming for a minimum of 3 days was required, and maximal numbers of PFC were obtained from spleen cells primed for 4 days. Depletion of T lymphocytes from Day 3-primed spleen cells abrogated LPS-mediated enhancement, and addition of concanavalin A supernatants to the T-cell depleted system restored the enhancement, suggesting that LPS action required co-operation with a product(s) of activated T cells. Addition of various interleukin-2 preparations including recombinant human IL-2 to the system restored the LPS-mediated enhancement. The response of Day 3 cells from which T cells were eliminated as vigorously as possible was similarly restored by the addition of IL-2, LPS and antigen, suggesting that IL-2 reacts directly with PFC precursors that have developed IL-2 receptors. LPS-mediated enhancement, in the presence or absence of T cells, was also markedly dependent on the presence of SRBC during in vitro culture. These data suggest that, in co-operation with IL-2 and other co-factors, antigen plays a significant role in driving the later stages of differentiation and/or division of PFC precursors to mature PFC.     

Immunosuppressive activity of macrophages in mice undergoing graft-versus-host reaction due to major histocompatibility complex class I plus II difference.

In a previous report, we showed that the injection of parental CD4+ T cells into major histocompatibility complex (MHC) class II disparate F1 hybrid mice induces autoimmune-like graft versus-host reaction (GVHR) resembling systemic lupus erythematosus (SLE) and the hepatic lesion of primary biliary cirrhosis (PBC). In the present study, we examined whether or not simultaneous or subsequent injection of CD8+ T cells changes the GVHR form. When parental CD8+ T cells together with CD4+ T cells were injected into MHC class I plus class II-disparate F1 mice, autoimmune phenomena did not develop and alternatively a profound immunosuppressive state was induced. Furthermore, ongoing autoimmune-like GVHR induced by CD4+ T cells was also suppressed by later injection of CD8+ T cells. In these mice, an increase of donor type CD8+ T cells and a marked decrease of host B and T cells in the spleen were observed. The spleen cells from these mice strongly inhibited the mitogenic response of normal spleen cells against lipopolysaccharide (LPS). In vitro studies demonstrated that this immunosuppression was not induced by CD8+ T cells themselves but by macrophages which produced suppressive factor(s) by LPS stimulation. These findings were discussed with reference to suppressive mechanisms of GVHR.     

Recirculating and sessile B cell populations in normal and CBA/N mice

Chromosomally distinguishable syngeneic mice were parabiosed and the resultant chimerism was followed for 6 weeks in the lymphoid organs, by culturing their cells with polyclonal mitogens, lipopolysaccharide (LPS) for B cells and phytohemagglutinin (PHA) for T cells. As expected of a recirculating population, the T cells equilibrated completely. The B cells in lymph nodes (LN) and Peyer's patches (PP) also equilibrated completely, suggesting that they too are recirculating. B cells in the spleen and blood, however, did not equilibrate over this period. After separation of parabiosed mice, the percentage of partner cells in both the recirculating T and B lymphocyte populations declined steadily, but it continued to rise in the LPS-responsive populations in spleen and peripheral blood suggesting that they were derived from precursor populations which were themselves chimeric. Injection of lymphocytes into CBA/Ca or CBA/N mice showed that LPS-responsive populations in LN and spleen localized differently. These results have been interpreted as demonstrating two major populations of LPS-responsive B lymphocytes in the mouse, one recirculating and the other sessile. The recirculating population appears to be the only LPS-responsive population in LN and PP. In the spleen, however, the recirculating cells constitute about a quarter of the LPS-responsive cells, while the rest are sessile cells. The relationship between these two populations has yet to be clarified. CBA/N mice are deficient in both populations but the sessile one appears to be more severely depleted.     

Immune unresponsiveness of spleen cells from lipopolysaccharide-treated mice to particulate thymus-dependent antigen. I. Evidence for differentiation signal defect

The cellular basis of the immune unresponsiveness induced by lipopolysaccharide (LPS) was analyzed at the B and T cell level. The immunosuppressive effect of LPS is not related to altered B cell competence. Inhibition of antibody responses was observed only for thymus-dependent (TD) and not for thymus-independent antigens. In the presence of T cell-replacing factor (TRF), LPS-sensitized B lymphocytes respond to TD antigenic stimulation and differentiate into antibody-forming cells. Evidence is presented for a decreased helper activity of LPS-sensitized T lymphocytes and for a defective production of TRF in concanavalin A-stimulated spleen cells from LPS-treated mice. The implication of a cell compartment other than T is discussed.     

Lipopolysaccharide from gram-negative bacteria enhances polyclonal B cell activation and exacerbates nephritis in MRL/lpr mice.

Depletion of B cells in mice bearing the lymphoproliferation (lpr) gene reduces lymphoproliferation and polyclonal B cell activation (PBA) and attenuates mononuclear cell vasculitis. We sought to verify whether the obverse was true, i.e. whether enhancement of B cell activity might exacerbate the nephritis of MRL/lpr (MRL) mice, a lupus-prone strain. The experimental approach was designed to address three questions: whether naturally occurring PBA in MRL mice could be further enhanced; whether enhanced PBA would exacerbate nephritis; and whether the mechanism of nephritis exacerbation involved interference with mononuclear phagocyte system (MPS) function. To enhance B cell activity, we injected MRL mice with lipopolysaccharide (LPS) from Gram-negative bacteria, a potent B cell activator. To determine whether nephritis was exacerbated, we performed immunopathologic studies and tests of renal function. To verify whether nephritis exacerbation involved impairment of MPS function, we probed the kinetics of immune complex removal from the circulation, their uptake by the liver and spleen, and their localization in kidney tissue. The results indicate that in MRL mice: (i) spontaneous PBA can be enhanced by LPS; (ii) enhancement of PBA by LPS exacerbates nephritis; and (iii) the MPS is already saturated, presumably due to excessive production of endogenous immune complexes. Thus, further increase in immune complex formation due to enhanced PBA by LPS results in increased localization of immune complexes in kidneys and exacerbated nephritis.     

Rheumatoid Synovial Fluid Reconstitutes the B-Cell Defect in CBA/N Mice

Synovial fluid from patients with rheumatoid arthritis (RA-SF) contains a biological activity which can replace T cells for activation of antibody secretion in human blood lymphoid cells and which can also induce the selective differentiation of IgG2b-secreting cells in lipopolysaccharide (LPS)-pre-activated mouse spleen cells. The B-cell activity of this factor was studied in CBA/N mice which have an X-linked B-cell immunodeficiency which manifests itself as a defective humoral response to certain thymus-independent antigens (TI-2). RA-SF has now been shown to reconstitute partly the B-cell deficiency in CBA/N splenic B cells in vitro. Addition of RA-SF to LPS-pretreated cell cultures results in IgG2b secretion in CBA/N spleen cells as well. In contrast to cells from normal CBA mice, cells from CBA/N mice cannot respond to interleukin 4 (IL-4) after addition of LPS with production of IgG1 antibodies in vitro. However, the addition of RA-SF completely restores a normal IL-4-induced IgG1 response. No other biologically active factors have been shown to allow the production of IgG antibody producing cells in CBA/N splenic B cells. It is postulated that the xid immunodeficiency could be the result of a deficient production of a biological activity which is abundant in RA-SF.     

Enhancement of the immune response in vitro by arsenic

We examined the effect of arsenic (As) on the immune response of mice to sheep erythrocytes, assaying the spleen for plaque-forming cells (PFC). The effect of As on the PFC response to sheep erythrocytes was dose-dependent. At high doses of As the PFC response was suppressed, whereas it enhanced the response at low doses. The suppression was due to the cytotoxic action of As against lymphocytes generally. On the other hand, enhancement was seen on the addition of As at the start of the culture or as a result of pretreatment of normal spleen cells with As. Even low doses of As were cytotoxic, to both B and T cells. They differed, however, in their susceptibility to As. When normal spleen cells were added to the culture of As-treated spleen cells, the enhancement of the PFC response was reversed. Suppressor-inducer B cells, in the normal spleen cells, could not induce suppressor T cells from As-treated spleen cells. And As did not affect suppressor T cells. These findings indicate that As deletes the precursors of suppressor T cells from normal spleen cells, and thus enhances the immune response.     

Expression of mouse CD43 in the B cell lineage of transgenic mice causes impaired immune responses to T-independent antigens

CD43 (leukosialin), a sialylated glycoprotein expressed on the surface of most hematopoietic cells, has been implicated in cell adhesion and signaling. However, its precise physiological function remains unclear. We used mouse CD43 (mCD43)-immunoglobulin enhancer-transgenic (TG) mice to study the role of mCD43 in vivo. Previous work revealed that mCD43 expression on mature B cells in these mice resulted in immunodeficiency to T-dependent (TD) antigens (Ag), possibly by impairing B-T cell interactions. In the present study we have immunized the TG mice with the T-independent (TI) Ag fluorescein-(Fl) lipopolysaccharide (LPS) (TI type 1 Ag) and Fl-Ficoll (TI type 2 Ag). Surprisingly, the mCD43-Ig enhancer expressing mice were impaired in their ability to mount humoral responses to both Fl-LPS and Fl-Ficoll, and had decreased numbers of cells responding to Ag in vivo. Flow cytometric analysis was performed on peritoneal B-1 cells, a population which often plays a major role in humoral responses to TI Ag such as bacterial Ag. This analysis revealed similar B220, IgM and CD5 expression patterns for the TG and nontransgenic (NTG) B-1 cells. In addition, purified peritoneal B-1 cells from TG and NTG mice were able to respond to LPS. Stimulation of splenic B cells in vitro with Fl-LPS and Fl-Ficoll revealed that, in contrast to NTG B cell responses, TG B cell responses could not be enhanced by co-culture with T cells. However, soluble T cell factor enhancement of the TG B cell responses was normal. These data suggest that the mCD43 expression on B cells may inhibit cell interactions that are important for enhanced TI Ag responses. The anti-adhesive forces of mucins in general may thus be critical in regulating both TD and TI humoral responses.     

B cell stimulating activity of seaweed extracts

The activity of seaweed extracts on murine and human lymphocytes was studied in vitro. The extracts of some kinds of seaweed, such as Hizikia fusiformis and Meristotheca papulosa, stimulated normal mouse spleen cells to proliferate. The responder cells are B cells, because the response was depleted by the treatment of spleen cells with anti-immunoglobulin (Ig) antibody and complement and being passed through a nylon wool column. This response is not due to lipopolysaccharide (LPS) contamination, because seaweed extracts can stimulate spleen cells of C3H/HeJ mice which are LPS low responders. Seaweed extracts also enhanced Ig production by B cells and tumor necrosis factor (TNF) production by macrophages. Furthermore, seaweed extracts stimulated human lymphocytes to proliferate. All these B cell stimulating activities of seaweed extracts associated with glycoproteins whose molecular weights resided in 100 kD. These results suggest that seaweed extracts have stimulating activity on B cells and macrophages and this ability could be used clinically for the modulation of immune responses.