Oral administration of soluble ß-glucans extracted from Grifola frondosa induces systemic antitumor immune response and decreases immunosuppression in tumor-bearing mice.

Maitake D (MD)-Fraction is a highly purified soluble ß-glucan derived from Grifola frondosa (an oriental edible mushroom). Intraperitoneal (i.p.) injection of MD-Fraction has been reported to inhibit tumor growth via enhancement of the host immune system. In this study, we demonstrated that oral administration of MD-Fraction as well as i.p. injection significantly inhibited tumor growth in murine tumor models. After oral administration, MD-Fraction was not transferred to the blood in its free form but was captured by antigen-presenting cells such as macrophages and dendritic cells (DCs) present in the Peyer's patch. The captured MD-Fraction was then transported to the spleen, thereby inducing the systemic immune response. Our study showed that MD-Fraction directly induced DC maturation via a C-type lectin receptor dectin-1 pathway. The therapeutic response of orally administered MD-Fraction was associated with (i) induced systemic tumor-antigen specific T cell response via dectin-1-dependent activation of DCs, (ii) increased infiltration of the activated T cells into the tumor and (iii) decreased number of tumor-caused immunosuppressive cells such as regulatory T cells and myeloid-derived suppressor cells. Our preclinical study suggests that MD-Fraction is a useful oral therapeutic agent in the management of patients with cancer.

A polysaccharide extracted from Grifola frondosa enhances the anti-tumor activity of bone marrow-derived dendritic cell-based immunotherapy against murine colon cancer.

We previously isolated the novel heteropolysaccharide maitake Z-fraction (MZF) from the maitake mushroom (Grifola frondosa), and demonstrated that MZF significantly inhibited tumor growth by inducing cell-mediated immunity. In this study, we demonstrated that MZF upregulated the expression of CD80, CD86, CD83, and MHC II on bone marrow-derived dendritic cells (DCs) and significantly increased interleukin-12 (IL-12) and tumor necrosis factor-alpha production by DCs in a dose-dependent manner. MZF-treated DCs significantly stimulated both allogeneic and antigen-specific syngenic T cell responses and enhanced antigen-specific interferon-gamma (IFN-gamma) production by syngenic CD4(+) T cells; however, MZF-treated DCs did not affect IL-4 production. Furthermore, the enhancement of IFN-gamma production in CD4(+) T cells, which was induced by MZF-treated DCs, was completely inhibited by the addition of an anti-IL-12 antibody. These results indicate that MZF induced DC maturation and antigen-specific Th1 response by enhancing DC-produced IL-12. We also demonstrated that DCs pulsed with colon-26 tumor lysate in the presence of MZF induced both therapeutic and preventive effects on colon-26 tumor development in BALB/c mice. These results suggest that MZF could be a potential effective adjuvant to enhance immunotherapy using DC-based vaccination.

Enhancement of cytotoxicity of NK cells by D-Fraction, a polysaccharide from Grifola frondosa.

In innate immunity, activated natural killer (NK) cells attack and damage pathogens such as bacteria and virus without restriction by the MHC antigen. NK cells activated by IL-12 have been reported to recognize and kill tumor cells in perforin-mediated apoptosis. We have reported that D-Fraction, a polysaccharide extracted from the maitake mushroom (Grifola frondosa), activates macrophages, dendritic cells, and T cells and inhibits the growth of tumor cells. However, the effects of D-Fraction on NK cell function in the innate immune response are not well known. In the present study, we administered D-Fraction to MM-46 mammary tumor-bearing C3H/HeJ mice intraperitoneally for 3 consecutive days and investigated its effects on the activation and cytotoxicity of NK cells. D-Fraction significantly enhanced the cytotoxicity against NK-sensitive YAC-1 cells and the expression of CD223 on NK cells. D-Fraction also increased the expression of CD86 on macrophages. In addition, the levels of IL-12 in the culture supernatant of whole spleen cells and in serum increased, compared with the control corresponding to an increase in expression of IL-12 receptor betaI on NK cells. These results suggest that D-Fraction enhances the cytotoxicity of NK cells through the production of IL-12 by macrophages activated by D-Fraction.

Maitake D-Fraction enhances antitumor effects and reduces immunosuppression by mitomycin-C in tumor-bearing mice.

OBJECTIVE: D-Fraction, a polysaccharide extracted from maitake mushrooms (Grifola frondosa), has been reported to exhibit an antitumor effect through activation of immunocompetent cells, including macrophages and T cells, with modulation of the balance between T-helper 1 and 2 cells. We examined whether D-Fraction could decrease the effective dosage of the chemotherapeutic agent, mitomycin-C (MMC), necessary to control carcinoma in mice. METHODS AND RESULTS: We determined that 0.25 mg.kg-1.d-1 was the optimal dosage of MMC because consecutive administration for 17 d resulted in antitumor effects and a survival ratio of 100% in mice bearing mammary cancer cells (MM-46). Although the dosage of MMC was lower than the effective level, spleen weight and total number of nuclear cells in the mouse spleen decreased, indicating that MMC showed immunosuppressive activity. In contrast, the combination of D-Fraction and MMC recovered the decreases in the dose response induced by MMC and inhibited tumor cell growth more than MMC alone. These effects were achieved through increased immunocompetent cell proliferation. We evaluated the expression of CD28 on splenic CD8+ T cells and the amount of interleukin-12 produced by whole spleen cells including macrophages after administering D-Fraction. The results showed enhancement of the T-helper 1 dominant response. CONCLUSION: These results suggest that D-Fraction can decrease the effective dosage in tumor-bearing mice by increasing the proliferation, differentiation, and activation of immunocompetent cells and thus provide a potential clinical benefit for patients with cancer.

Soluble ß-glucan from Grifola frondosa induces tumor regression in synergy with TLR9 agonist via dendritic cell-mediated immunity.

The maturation of dendritic cells into more-immunostimulatory dendritic cells by stimulation with different combinations of immunologic agents is expected to provide efficient, adoptive immunotherapy against cancer. Soluble ß-glucan maitake D-fraction, extracted from the maitake mushroom Grifola frondosa, acts as a potent immunotherapeutic agent, eliciting innate and adoptive immune responses, thereby contributing to its antitumor activity. Here, we evaluated the efficacy of maitake D-fraction, in combination with a Toll-like receptor agonist, to treat tumors in a murine model. Our results showed that maitake D-fraction, in combination with the Toll-like receptor 9 agonist, cytosine-phosphate-guanine oligodeoxynucleotide, synergistically increased the expression of dendritic cell maturation markers and interleukin-12 production in dendritic cells, but it did not increase interleukin-10 production, generating strong effector dendritic cells with an augmented capacity for efficiently priming an antigen-specific, T helper 1-type T cell response. Maitake D-fraction enhances cytosine-phosphate-guanine oligodeoxynucleotide-induced dendritic cell maturation and cytokine responses in a dectin-1-dependent pathway. We further showed that a combination therapy using cytosine-phosphate-guanine oligodeoxynucleotide and maitake D-fraction was highly effective, either as adjuvants for dendritic cell vaccination or by direct administration against murine tumor. Therapeutic responses to direct administration were associated with increased CD11c(+) dendritic cells in the tumor site and the induction of interferon-γ-producing CD4(+) and CD8(+) T cells. Our results indicate that maitake D-fraction and cytosine-phosphate-guanine oligodeoxynucleotide synergistically activated dendritic cells, resulting in tumor regression via an antitumor T helper cell 1-type response. Our findings provide the basis for a potent antitumor therapy using a novel combination of immunologic agents for future clinical immunotherapy studies in patients.

Relationship between dendritic cells and the D-fraction-induced Th-1 dominant response in BALB/c tumor-bearing mice.

Dendritic cells (DCs) are known to not only induce the activation of T cells, but are also associated with the differentiation of T cells. The D-fraction, a beta-glucan extracted from maitake (Grifola frondosa) which expresses anti-tumor effects by establishing a helper (Th)-1 dominance in BALB/c mice, enhanced IL-12p70 production by DCs, when the ratio of CD8alpha(+) DCs to CD8alpha(-) DCs increased. In addition, examination of the tumor rejection effect of D-fraction-stimulated DCs loaded with tumor antigen revealed that tumor growth is inhibited completely by activating CD4(+) T cells and CD8(+) T cells.

Can maitake MD-fraction aid cancer patients?

Maitake mushroom (Grifola frondosa) MD-fraction containing beta-1,6 glucan with beta-1,3 branched chains has previously exhibited strong anticancer activity by increasing immune-competent cell activity.1,2 In this non-random case series, a combination of MD-fraction and whole maitake powder was investigated to determine its effectiveness for 22- to 57-year-old cancer patients in stages II-IV. Cancer regression or significant symptom improvement was observed in 58.3 percent of liver cancer patients, 68.8 percent of breast cancer patients, and 62.5 percent of lung cancer patients. The trial found a less than 10-20 percent improvement for leukemia, stomach cancer, and brain cancer patients. Furthermore, when maitake was taken in addition to chemotherapy, immune-competent cell activities were enhanced 1.2-1.4 times, compared with chemotherapy alone. Animal studies have supported the use of maitake MD-fraction for cancer.

Effect of Maitake (Grifola frondosa) D-Fraction on the activation of NK cells in cancer patients.

Maitake D-Fraction, extracted from maitake mushroom, has been reported to exert its antitumor effect in tumor-bearing mice by enhancing the immune system through activation of macrophages, T cells, and natural killer (NK) cells. In a previous study, the combination of immunotherapy with the maitake D-Fraction and chemotherapy suggested that the D-Fraction may have the potential to decrease the size of lung, liver, and breast tumors in cancer patients. In the present study, we administered maitake D-Fraction to cancer patients without anticancer drugs, and at the same time NK cell activity was monitored to investigate whether the activity is closely related with disease progression. The numbers of CD4(+) and CD8(+) cells in the peripheral blood were measured in 10 patients, and NK cell activity was assessed using K-562 cells as target cells. Serum soluble interleukin-2 receptor (sIL-2R) levels in three patients and the expression of tumor markers in four patients were determined by enzyme-linked immunosorbent assay. The slight changes observed in the CD4(+) and CD8(+) cell numbers were independent of disease severity or stage as well as serum sIL-2R levels. In contrast, maitake D-Fraction hindered metastatic progress, lessened the expression of tumor markers, and increased NK cell activity in all patients examined. Thus maitake D-Fraction appears to repress cancer progression and primarily exerts its effect through stimulation of NK activity. In addition, we conclude that measurement of NK cell activity may be a useful clinical parameter in monitoring disease progression during and following immunotherapy with maitake D-Fraction.

Administration of a polysaccharide from Grifola frondosa stimulates immune function of normal mice.

We have reported that D-Fraction, a polysaccharide extracted from the edible maitake mushroom (Grifola frondosa), activates immunocompetent cells, thereby eliciting antitumor activity. To extend the application of D-Fraction as a nutritional supplement for healthy people as well as treatment for those with cancer, we investigated the effects of D-Fraction on the immune system in normal C3H/HeJ mice. Splenocytes from mice administered D-Fraction intraperitoneally for 17 consecutive days were cultured, and the culture supernatants were analyzed for nitric oxide (NO) and interleukin (IL)-12 production by antigen-presenting cells (APCs), including macrophages and dendritic cells, and also for the T helper (Th)-1 cytokine interferon (IFN)-gamma and the Th-2 cytokines IL-4 and IL-10. The level of IL-10 as well as those of NO and IFN-gamma were increased by D-Fraction as compared with the control, in which the serum immunoglobulin E level was increased. The results suggest that D-Fraction induced a Th-2 dominant response through the activation of macrophages, resulting in the enhancement of humoral immunity rather than cell-mediated immunity. Furthermore, an increase in the percentage ratio of CD69 and CD89 expression on major histocompatibility complex II(+) cells revealed activation of APCs 4 h after D-Fraction administration. These results indicate that D-Fraction enhances both the innate and adaptive arms of the immune response in normal mice. Therefore, its administration may enhance host defense against foreign pathogens and protect healthy individuals from infectious diseases.

Soluble ß-glucan from Grifola frondosa induces proliferation and Dectin-1/Syk signaling in resident macrophages via the GM-CSF autocrine pathway.

MD-Fraction, a highly purified, soluble ß-(1,3) (1,6)-glucan obtained from Grifola frondosa (an oriental edible mushroom), has been reported to inhibit tumor growth by modulating host immunity. ß-Glucan, a major component of the fungal cell wall, is generally recognized by PRRs expressed on macrophages and DCs, such as Dectin-1, and the ability of ß-glucans to modulate host immunity is influenced by their structure and purity. Most cellular studies have used particulate ß-glucans, such as yeast zymosan (crude ß-glucan) and curdlan (purified ß-glucan). However, little is known about the cellular mechanism of soluble ß-glucans, including MD-Fraction, despite significant therapeutic implications. In this study, we investigated the cellular mechanism of MD-Fraction in murine resident macrophages and compared it with two well-known ß-glucan particles. MD-Fraction induced GM-CSF production rapidly through Dectin-1-independent ERK and p38 MAPK activation. Subsequently, MD-Fraction-induced GM-CSF enhanced proliferation and Dectin-1 expression, which permitted Dectin-1-mediated TNF-α induction through the Syk pathway. Curdlan induced not only the proliferation and activation of Dectin-1/Syk signaling in a manner similar to MD-Fraction but also the uncontrolled, proinflammatory cytokine response. Contrastingly, zymosan reduced proliferation and Dectin-1 expression significantly, indicating that the mechanism of macrophage activation by MD-Fraction differs from that of zymosan. This is the first study to demonstrate that purified ß-glucans, such as MD-Fraction and curdlan, induce GM-CSF production directly, resulting in Dectin-1/Syk activation in resident macrophages. In conclusion, we demonstrated that MD-Fraction induces cell proliferation and cytokine production without excessive inflammation in resident macrophages, supporting its immunotherapeutic potential.

Potential antitumor activity of a low-molecular-weight protein fraction from Grifola frondosa through enhancement of cytokine production.

Edible mushrooms contain an abundance of immune-enhancing nutritients. Some of these compounds, referred to as biological response modifiers (BRMs), have been used in biological therapies for cancer treatment. We obtained a low-molecular-weight protein fraction (MLP-Fraction) from the fruiting body of the maitake mushroom Grifola frondosa by multiple sequential steps, including ethanol precipitation, DEAE-exchange chromatography, and gel filtration. The effect of the MLP-Fraction on the immune system was determined using normal mice. This resulted in a simultaneous increase in splenocyte proliferation and production of cytokines such as interleukin (IL)-1alpha, tumor necrosis factor-alpha, IL-10, IL-12, and interferon (IFN)-gamma. The expression levels of IFN-gamma and IL-12 in antigen-presenting cells (APCs) and the activation of natural killer (NK) cells, macrophages, and dendritic cells were observed. These results suggest a mechanism in which NK cells are activated through cytokines produced by APCs. We also confirmed the possibility that the MLP-Fraction acts as a BRM using colon-26 carcinoma-bearing mice. This fraction enhanced the production of IL-12 and IFN-gamma by splenocytes in tumor-bearing mice and clearly showed an inhibitory effect on tumor cell growth.

Parathyroid hormone-related protein has an anorexigenic activity via activation of hypothalamic urocortins 2 and 3.

Cancer cachexia is reported to be a major cause of cancer-related death. Since the pathogenesis is not entirely understood, only few effective therapies have been established. Since myriad tumors produce parathyroid hormone-related protein (PTHrP), plasma concentrations of PTHrP are increased in cancer cachexia. We measured the food intake, gastric emptying, conditioned taste aversion (CTA), and gene expression of hypothalamic neuropeptides in mice after administering PTHrP intraperitoneally. We administered PTHrP intravenously in rats and examined the gastroduodenal motility and vagal nerve activities. We also examined whether chronic administration of PTHrP influenced the food intake and body weight. Peripherally administered PTHrP induced negative energy balance by decreasing the food intake and gastric emptying; however, it did not induce CTA. The mechanism involved the activation of hypothalamic urocortins 2 and 3 through vagal afferent pathways and the suppression of gastroduodenal motor activity. The continuous infusion of PTHrP reduced the food intake and body weight gain with a concomitant decrease in the fat and skeletal muscle. Our findings suggest that PTHrP influences the food intake and body weight; therefore, PTHrP can be considered as a therapeutic target for cancer cachexia.

Characterization and antitumor effect of a novel polysaccharide from Grifola frondosa.

A novel polysaccharide, MZF, with a molecular mass of 23 kDa was isolated from Grifola frondosa . Results from methylation and (1)H NMR led to the conclusion that MZF is a heteropolysaccharide consisting of -->6)-alpha-D-Galp-(1--> (36.2%), -->3)-alpha-L-Fucp-(1--> (14.5%), -->6)-alpha-D-Manp-(1--> (9.4%), -->3)-beta-D-Glcp-(1--> (10.1%), alpha-D-Manp-(1--> (23.2%), and -->3,6)-beta-D-Glcp-(1--> (6.5%). Although MZF did not affect the proliferation of colon-26 cells in vitro, it significantly inhibited tumor growth in BALB/cA mice inoculated with colon-26 cancer cells. Moreover, MZF significantly induced the proliferation of splenocytes and peritoneal macrophages. The mRNA expression of IL-12p40, IL-2 and IFN-gamma were increased significantly in MZF-treated spleen. Furthermore, MZF augmented the percentage of IFN-gamma-producing cells in both splenic CD4(+) and CD8(+) T cells and tumor infiltrating CD4(+) and CD8(+) T cells and enhanced the cytotoxic activity of NK cells and CTLs. These results indicate that MZF is a novel effective immunomodulator that has antitumor activity associated with induced cell-mediated immunity.

Maitake beta-glucan enhances therapeutic effect and reduces myelosupression and nephrotoxicity of cisplatin in mice.

Cisplatin is broadly used clinically as an anticancer drug. Despite its significant anticancer activity, cisplatin-induced nephrotoxicity and myelosuppression limit its use. MD-Fraction is glucan purified from maitake (Grifola frondosa), which has beta-1, 6-main chain with beta-1, 3-branches, has been reported to exhibit antitumor and antimetastatic activities by enhancing the immune system. In this study, we demonstrate that MD-Fraction in combination with cisplatin significantly enhanced antitumor and antimetastatic activity compared to cisplatin alone. MD-Fraction reduced decreases in body weight, spleen weight and the number of immunocompetent cells such as macrophages, DCs and NK cells in cisplatin-treated mice. MD-Fraction also induced IL-12p70 production by splenocytes, resulting in increased NK cell activity in cisplatin-treated mice. MD-Fraction significantly increased the mRNA expression of GM-CSF, G-CSF, M-CSF, IFN-gamma, IL-12 p40 in splenocytes and reduced the decrease in the number of CFU-GM colonies in cisplatin-treated bone marrow. These facts suggest that MD-Fraction can reduce cisplatin-induced myelosuppression. Moreover, treatment with MD-Fraction significantly reduced cisplatin-induced nephrotoxicity accompanied by increases in serum creatinine level, necrosis and apoptosis of renal tubular cells. These results suggest that MD-Fraction in combination with cisplatin cannot only enhance antitumor and antimentastatic acitivity, but also reduce cisplatin-induced myelotoxicity and nephrotoxicity.

Maitake beta-glucan enhances granulopoiesis and mobilization of granulocytes by increasing G-CSF production and modulating CXCR4/SDF-1 expression.

Previous studies have presented that Maitake beta-glucan (MD-Fraction) extracted from the fruit body of Grifola frondosa has an anti-tumor effect by activating the immune system. Recently, the stimulating effects of beta-glucans on hematopoiesis were identified as new characteristics of polysaccharides, possibly helping to relieve the immunosuppression which results from chemotherapies. We demonstrated that the production of granulocyte colony-stimulating factor (G-CSF) was significantly enhanced by MD-Fraction (8mg/kg, i.p.) in granulocytopenic model induced in mice using cyclophosphamide (200mg/kg, i.p.). In addition, MD-Fraction induced a biphasic increase in the number of granulocytes in the spleen. The mechanism for the increase in granulocytes on the early phase on day 1 might involve the increased mRNA expression of macrophage inflammatory protein-2 (MIP-2), in the splenic cells, thereby recruiting granulocytes into the spleen. Interestingly, a decline of myeloid progenitors in the bone marrow and an increase in granulocytes in the peripheral blood were observed on day 5, suggesting a mobilization of granulocytes and their progenitors from the bone marrow to the peripheral blood. We confirmed that a possible mechanism in which MD-Fraction promoted the mobilization of granulocytes and their progenitors from the bone marrow is down-regulating the expression of the chemokine receptor, CXCR4, and its ligand, stromal cell-derived factor 1 (SDF-1) in the bone marrow microenvironment. These results reveal a novel function of Maitake beta-glucan that enhances the granulopoiesis and mobilization of granulocytes and their progenitors by stimulating G-CSF production. This finding presents opportunities to develop new therapeutic strategies against the immunosuppression caused by chemotherapies in cancer patients.

Inhibitory effect of MD-Fraction on tumor metastasis: involvement of NK cell activation and suppression of intercellular adhesion molecule (ICAM)-1 expression in lung vascular endothelial cells.

The anti-metastatic activity of MD-Fraction extracted from the maitake mushroom (Grifola frondosa) was examined in an experimental murine model of lung metastasis. Intraperitoneal administration of MD-Fraction 2 d before tumor implantation significantly inhibited lung metastasis of colon-26 carcinoma and B16/BL6 melanoma cells. In this model, MD-Fraction enhanced IL-12 production from antigen presenting cells (APCs). MD-Fraction treatment activated NK cells and increased cytotoxicity against YAC-1 and colon-26 carcinoma cells. Furthermore, the depletion of NK cells with anti-asialo GM1 abolished the inhibitory effect of MD-Fraction on lung metastasis of colon-26 cells. Ex vivo, B16/BL6 cell adhesion to LPS-activated murine lung vascular endothelial cells was inhibited by MD-Fraction and anti-intercellular adhesion molecule (ICAM)-1 antibody. These results suggest that MD-Fraction inhibits tumor metastasis by activating NK cells and APCs, and by suppressing of ICAM-1 leading to the inhibition of tumor cell adhesion to vascular endothelial cells.

Effect of maitake (Grifola frondosa) D-fraction on the control of the T lymph node Th-1/Th-2 proportion.

We have already reported that the D-Fraction, a beta-glucan extracted from the fruiting body of the maitake mushroom (Grifola frondosa), activates cellular immunity and expresses anti-tumor effects. In this study we investigated the anti-tumor functions of D-Fraction in relation to its control of the balance between T lymphocyte subsets Th-1 and Th-2. D-Fraction decreased the activation of B cells and potentiated the activation of helper T cells, resulting in enhanced cellular immunity. It also induced the production of interferon (IFN)-gamma, interleukin (IL)-12 p70, and IL-18 by whole spleen cells and lymph node cells, but suppressed that of IL-4. These results suggest that D-Fraction establishes Th-1 dominance which induces cellular immunity in the population that was Th-2 dominant due to carcinoma.

A polysaccharide, extract from Grifola frondosa, induces Th-1 dominant responses in carcinoma-bearing BALB/c mice.

A polysaccharide, designated as the D-fraction, extracted from maitake (Grifola frondosa), was reported to have anti-tumor effects by activating macrophages and T cells in C3H/HeN mice in which a Th-1 dominant response was established. In this study using BALB/c mice in which a Th-2 response is genetically dominant, D-fraction reduced the expression of Th-2 cytokine interleukin (IL)-4 but markedly increased the expression of Th-1 cytokine interferon (IFN)-gamma in CD4(+) T cells and also increased IL-12p70 production as well as IFN-gamma production by antigen-presenting cells (APCs), suggesting that D-fraction promotes the differentiation into Th-1 cells of CD4(+) T cells through enhancement of IL-12p70 production by APCs.

Effects of D-Fraction, a polysaccharide from Grifola frondosa on tumor growth involve activation of NK cells.

Natural killer (NK) cells are directly cytotoxic for tumor cells and play a primary role in regulating immune responses. We monitored levels of NK cell cytotoxic activity in cancer patients receiving D-Fraction extracted from maitake mushrooms (Grifola frondosa). Elevated levels of cytotoxic activity were maintained for one year. To elucidate the mechanisms underlying long-term activation of NK cells during treatment with D-Fraction, we examined tumor volume and levels of IFN-gamma and TNF-alpha in MM46-bearing C3H/HeN mice to which D-Fraction was administered for 19 d. D-Fraction markedly suppressed tumor growth, corresponding with increases in TNF-alpha and IFN-gamma released from spleen cells and a significant increase in TNF-alpha expressed in NK cells. This suggests that the D-Fraction activates NK cells even on the 20th day after treatment. Furthermore, D-Fraction increased macrophage-derived interleukin (IL)-12, which serves to activate NK cells. These results suggest that NK cells are not only responsible for the early effects of D-Fraction on tumor growth, but also for the long-term tumor-suppressive effects of D-Fraction through increased IL-12 released from macrophages.