B-1 cell-mediated modulation of M1 macrophage profile ameliorates microbicidal functions and disrupt the evasion mechanisms of Encephalitozoon cuniculi.

Here, we have investigated the possible effect of B-1 cells on the activity of peritoneal macrophages in E. cuniculi infection. In the presence of B-1 cells, peritoneal macrophages had an M1 profile with showed increased phagocytic capacity and index, associated with the intense microbicidal activity and a higher percentage of apoptotic death. The absence of B-1 cells was associated with a predominance of the M2 macrophages, reduced phagocytic capacity and index and microbicidal activity, increased pro-inflammatory and anti-inflammatory cytokines production, and higher percentual of necrosis death. In addition, in the M2 macrophages, spore of phagocytic E. cuniculi with polar tubular extrusion was observed, which is an important mechanism of evasion of the immune response. The results showed the importance of B-1 cells in the modulation of macrophage function against E. cuniculi infection, increasing microbicidal activity, and reducing the fungal mechanisms involved in the evasion of the immune response.

Study of tissue inflammatory response in different mice strains infected by dematiaceous fungi Fonsecaea pedrosoi.

BACKGROUND: Diseases caused by melanized fungi include mycetoma, chromoblastomycosis and phaeohyphomycosis. This broad clinical spectrum depends on the dynamic interactions between etiologic agent and host. The immune status of the host influences on the development of the disease, as, an exemple. phaeohyphomicosis is more frequently observed in immunocompromised patients. OBJECTIVES: Examine the histological inflammatory response induced by Fonsecaea pedrosoi in several different strains of mice (BALB/c, C57BL/6, Nude and SCID, and reconstituted Nude). METHODS: Fonsecaea pedrosoi was cultivated on agar gel and a fragment of this gel was implanted subcutaneously in the abdominal region of female adult mice. After infection has been obtained, tissue fragment was studied histopathologically. RESULTS: There were significant changes across the strains, with the nodular lesion more persistent in Nude and SCID mice, whereas in immunocompetent mice the lesion progressed to ulceration and healing. The histopathological analysis showed a significant acute inflammatory reaction which consisted mainly of neutrophils in the initial phase that was subsequently followed by a tuberculoid type granuloma in immunocompetent mice. STUDY LIMITATIONS: There is no a suitable animal model for chromoblastomycosis. CONCLUSIONS: The neutrophilic infiltration had an important role in the containment of infection to prevent fungal spreading, including in immunodeficient mice. The fungal elimination was dependent on T lymphocytes. The re-exposure of C57BL/6 mice to Fonsecaea pedrosoi caused a delay in resolving the infection, and appearance of muriform cells, which may indicate that re-exposure to fungi, might lead to chronicity of infection.

Study of tissue inflammatory response in different mice strains infected by dematiaceous fungi Fonsecaea pedrosoi

Abstract: Background: Diseases caused by melanized fungi include mycetoma, chromoblastomycosis and phaeohyphomycosis. This broad clinical spectrum depends on the dynamic interactions between etiologic agent and host. The immune status of the host influences on the development of the disease, as, an exemple. phaeohyphomicosis is more frequently observed in immunocompromised patients. Objectives: Examine the histological inflammatory response induced by Fonsecaea pedrosoi in several different strains of mice (BALB/c, C57BL/6, Nude and SCID, and reconstituted Nude). Methods: Fonsecaea pedrosoi was cultivated on agar gel and a fragment of this gel was implanted subcutaneously in the abdominal region of female adult mice. After infection has been obtained, tissue fragment was studied histopathologically. Results: There were significant changes across the strains, with the nodular lesion more persistent in Nude and SCID mice, whereas in immunocompetent mice the lesion progressed to ulceration and healing. The histopathological analysis showed a significant acute inflammatory reaction which consisted mainly of neutrophils in the initial phase that was subsequently followed by a tuberculoid type granuloma in immunocompetent mice. Study limitations: There is no a suitable animal model for chromoblastomycosis. Conclusions: The neutrophilic infiltration had an important role in the containment of infection to prevent fungal spreading, including in immunodeficient mice. The fungal elimination was dependent on T lymphocytes. The re-exposure of C57BL/6 mice to Fonsecaea pedrosoi caused a delay in resolving the infection, and appearance of muriform cells, which may indicate that re-exposure to fungi, might lead to chronicity of infection.

B-1 cell-mediated modulation of M1 macrophage profile ameliorates microbicidal functions and disrupt the evasion mechanisms of Encephalitozoon cuniculi

Here, we have investigated the possible effect of B-1 cells on the activity of peritoneal macrophages in E. cuniculi infection. In the presence of B-1 cells, peritoneal macrophages had an M1 profile with showed increased phagocytic capacity and index, associated with the intense microbicidal activity and a higher percentage of apoptotic death. The absence of B-1 cells was associated with a predominance of the M2 macrophages, reduced phagocytic capacity and index and microbicidal activity, increased pro-inflammatory and anti-inflammatory cytokines production, and higher percentual of necrosis death. In addition, in the M2 macrophages, spore of phagocytic E. cuniculi with polar tubular extrusion was observed, which is an important mechanism of evasion of the immune response. The results showed the importance of B-1 cells in the modulation of macrophage function against E. cuniculi infection, increasing microbicidal activity, and reducing the fungal mechanisms involved in the evasion of the immune response

B-1 cell-mediated modulation of M1 macrophage profile ameliorates microbicidal functions and disrupt the evasion mechanisms of Encephalitozoon cuniculi

Here, we have investigated the possible effect of B-1 cells on the activity of peritoneal macrophages in E. cuniculi infection. In the presence of B-1 cells, peritoneal macrophages had an M1 profile with showed increased phagocytic capacity and index, associated with the intense microbicidal activity and a higher percentage of apoptotic death. The absence of B-1 cells was associated with a predominance of the M2 macrophages, reduced phagocytic capacity and index and microbicidal activity, increased pro-inflammatory and anti-inflammatory cytokines production, and higher percentual of necrosis death. In addition, in the M2 macrophages, spore of phagocytic E. cuniculi with polar tubular extrusion was observed, which is an important mechanism of evasion of the immune response. The results showed the importance of B-1 cells in the modulation of macrophage function against E. cuniculi infection, increasing microbicidal activity, and reducing the fungal mechanisms involved in the evasion of the immune response

The axis IL-10/claudin-10 is implicated in the modulation of aggressiveness of melanoma cells by B-1 lymphocytes.

B-1 lymphocytes are known to increase the metastatic potential of B16F10 melanoma cells via the extracellular signal-regulated kinase (ERK) pathway. Since IL-10 is associated with B-1 cells performance, we hypothesized that IL-10 could be implicated in the progression of melanoma. In the present work, we found that the C57BL/6 mice, inoculated with B16F10 cells that were co-cultivated with B-1 lymphocytes from IL-10 knockout mice, developed fewer metastatic nodules than the ones which were injected with the melanoma cells that were cultivated in the presence of wild-type B-1 cells. The impairment of metastatic potential of the B16F10 cells was correlated with low activation of the ERK signaling pathway, supporting the idea that the production of IL-10 by B-1 cells influences the behavior of the tumor. A microarray analysis of the B-1 lymphocytes revealed that IL-10 deficiency is associated with down-regulation of the genes that code for claudin-10, a protein that is involved in cell-to-cell contact and that has been linked to lung adenocarcinoma. In order to determine the impact of claudin-10 in the cross-talk between B-1 lymphocytes and the B16F10 tumor cells, we took advantage of small interfering RNA. The silencing of claudin-10 gene in B-1 lymphocytes inhibited activation of the ERK pathway and abrogated the B-1-induced aggressive behavior of the B16F10 cells. Thus, our findings suggest that the axis IL-10/claudin-10 is a promising target for the development of therapeutic agents against aggressive melanoma.

Evaluation of Experimental Infection with L. ( L.) Amazonensis in X-Linked Immunodeficient Mice.

B-1 cells are a subtype of B cells with peculiar characteristics. These cells are distinct from B-2 lymphocytes in their morphology, ontogeny, tissue distribution, and phenotypic functional features. B-1 cells can participate in the immune response in several ways, for example, by being recruited to inflammatory foci, producing large amounts of IL-10 cytokine, and differentiating into IgM-secreting cells or phagocytes. Nevertheless, the role of B-1 cells in the pathogenesis of experimental leishmaniasis has not been fully elucidated. Here we evaluated the role of B-1 cells in Leishmania ( L.) amazonensis infection using X-linked immunodeficient (XID) mice that possess a mutation in Bruton's tyrosine kinase (Btk) that leads to a reduced number of B-1 cells. The course of infection and the corresponding immune response were analyzed in infected mice. XID mice showed an increase in parasite number in paws, lymph nodes, and spleen compared to BALB/c infected controls. Infected XID mice had higher IL-10 levels and lower anti- Leishmania IgM. The adoptive transfer of peritoneal B-1 cells into XID mice restored peritoneal B-1 cells and parasite burden in the footpad in a pattern similar to that observed in the BALB/c controls at 10 wk. Our results demonstrate the higher susceptibility of XID mice to infection with L. ( L.) amazonensis compared to controls. In addition, we show that the presence of B-1 cells contributes to improved animal resistance to parasites, suggesting that these cells are involved in the control of cutaneous infection caused by L. ( L.) amazonensis.

Effects of drinking desalinated seawater on cell viability and proliferation.

Desalination of seawater is becoming an important means to address the increasing scarcity of freshwater resources in the world. Seawater has been used as drinking water in the health, food, and medical fields and various beneficial effects have been suggested, although not confirmed. Given the presence of 63 minerals and trace elements in drinking desalinated seawater (63 DSW), we evaluated their effects on the behavior of tumorigenic and nontumorigenic cells through the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and annexin-V-fluorescein isothiocyanate/propidium iodide staining. Our results showed that cell viability and proliferation in the presence of 63 DSW were significantly greater than in mineral water and in the presence of fetal bovine serum in a dose-dependent manner. Furthermore, 63 DSW showed no toxic effect on murine embryonic fibroblast (NIH-3T3) and murine melanoma (B16-F10) cells. In another assay, we also showed that pre-treatment of non-adherent THP-1 cells with 63 DSW reduces apoptosis incidence, suggesting a protective effect against cell death. We conclude that cell viability and proliferation were improved by the mineral components of 63 DSW and this effect can guide further studies on health effects associated with DSW consumption.

B-1 cell decreases susceptibility to encephalitozoonosis in mice.

Encephalitozoon cuniculi is an opportunist intracellular pathogen of mammals. The adaptive immune response is essential to eliminate E. cuniculi, but evidence is mounting that the response initiated by the innate immune response may ultimately define whether or not the parasite can survive. B-1 cells may act as antigen-presenting cells or differentiate into phagocytes, playing different roles in many infection models. However, the role of these cells in the dynamics of Encephalitozoon sp. infections is still unknown. To investigate the role of B-1 cells in E. cuniculi infection, BALB/c and BALB/c XID (B-1 cells deficient) mice were infected with E. cuniculi spores. Cytometric analyses of peritoneal cells showed that B-1 cells and macrophages increased significantly in infected BALB/c mice compared to uninfected controls. Despite the increase in the number of CD4+ and CD8+ lymphocytes in XID mice, these animals were more susceptible to infection as evidenced histologically with more prominent inflammatory lesions and parasite burden. Pro-inflammatory cytokines increased in both infected BALB/c and BALB/c XID mice. To confirm B-1 cells role in encephalitozoonosis, we adoptively transferred B-1 cells to BALB/c XID mice and this group showed few symptoms and microscopic lesions, associated with an increased in cytokines. Together, these results suggest that B-1 cells may increase the resistance of BALB/c mice to encephalitozoonosis, evidencing for the first time the important role of B-1 lymphocytes in the control of microsporidia infection.

B-1 cell decreases susceptibility to encephalitozoonosis in mice

Encephalitozoon cuniculi is an opportunist intracellular pathogen of mammals. The adaptive immune response is essential to eliminate E. cuniculi, but evidence is mounting that the response initiated by the innate immune response may ultimately define whether or not the parasite can survive. B-1 cells may act as antigen-presenting cells or differentiate into phagocytes, playing different roles in many infection models. However, the role of these cells in the dynamics of Encephalitozoon sp. infections is still unknown. To investigate the role of B-1 cells in E. cuniculi infection, BALB/c and BALB/c XID (B-1 cells deficient) mice were infected with E. cuniculi spores. Cytometric analyses of peritoneal cells showed that B-1 cells and macrophages increased significantly in infected BALB/c mice compared to uninfected controls. Despite the increase in the number of CD4(+) and CD8(+) lymphocytes in XID mice, these animals were more susceptible to infection as evidenced histologically with more prominent inflammatory lesions and parasite burden. Pro-inflammatory cytokines increased in both infected BALB/c and BALB/c XID mice. To confirm B-1 cells role in encephalitozoonosis, we adoptively transferred B-1 cells to BALB/c XID mice and this group showed few symptoms and microscopic lesions, associated with an increased in cytokines. Together, these results suggest that B-1 cells may increase the resistance of BALB/c mice to encephalitozoonosis, evidencing for the first time the important role of B-1 lymphocytes in the control of microsporidia infection.

Propionibacterium acnes induces an adjuvant effect in B-1 cells and affects their phagocyte differentiation via a TLR2-mediated mechanism.

B-1 lymphocytes are present in large numbers in the mouse peritoneal cavity, as are macrophages, and are responsible for natural IgM production. These lymphocytes migrate to inflammatory foci and are also involved in innate immunity. It was also demonstrated that B-1 cells are able to differentiated into phagocytes (B-1CDP), which is characterized by expression of F4/80 and increased phagocytic activity. B-1 cell responses to antigens and adjuvants are poorly characterized. It has been shown that Propionibacterium acnes suspensions induce immunomodulatory effects in both macrophages and B-2 lymphocytes. We recently demonstrated that this bacterium has the ability to increase B-1 cell populations both in vitro and in vivo. P. acnes induces B-1CDP differentiation, increases the expression of TLR2, TLR4 and TLR9 and augments the expression of CD80, CD86 and CD40 in B-1 and B-1CDP cells. Because P. acnes has been shown to modulate TLR expression, in this study, we investigated the role of TLR2 and TLR4 in B-1 cell population, including B-1CDP differentiation and phagocytic activity in vitro and in vivo. Interestingly, we have demonstrated that TLR2 signaling could be involved in the increase in the B-1 cell population induced by P. acnes. Furthermore, the early differentiation of B-1CDP is also dependent of TLR2. It was also observed that TLR signals also interfere in the phagocytic ability of B-1 cells and their phagocytes. According to these data, it is clear that P. acnes promotes an important adjuvant effect in B-1 cells by inducing them to differentiate into B-1CDP cells and modulates their phagocytic functions both in vivo and in vitro. Moreover, most of these effects are mediated primarily via TLR2. These data reinforce the findings that such bacterial suspensions have powerful adjuvant properties. The responses of B-1 cells to exogenous stimulation indicate that these cells are important to the innate immune response.

An Overview of B-1 Cells as Antigen-Presenting Cells.

The role of B cells as antigen-presenting cells (APCs) has been extensively studied, mainly in relation to the activation of memory T cells. Considering the B cell subtypes, the role of B-1 cells as APCs is beginning to be explored. Initially, it was described that B-1 cells are activated preferentially by T-independent antigens. However, some reports demonstrated that these cells are also involved in a T-dependent response. The aim of this review is to summarize information about the ability of B-1 cells to play a role as APCs and to briefly discuss the role of the BCR and toll-like receptor signals in this process. Furthermore, some characteristics of B-1 cells, such as natural IgM production and phagocytic ability, could interfere in the participation of these cells in the onset of an adaptive response.

Ikaros could be a key factor in the maintenance of "B-side" of B-1 cells.

Ikaros, a zinc finger transcription factor, is an important regulator of the hematopoietic system. Several studies have suggested the role of Ikaros in the development, maturation, activation and differentiation of lymphocytes. To elucidate this mechanism, it is important to understand how this transcription factor works in the dichotomy of the hematopoietic system, a topic that remains uncertain. Herein, we investigated the role of Ikaros in the control of the lymphomyeloid phenotype of B-1 lymphocytes. We found that Ikaros, as well as its target genes, are expressed in B-1 cells,. Moreover, Ikaros positively regulates the expression of Flt3, Gfi and Il7r, while it down-regulates PU.1. During the induction of differentiation of B-1 cells toward phagocytes, Ikaros transcription was reduced. Taken together, these data pointed to the relevance of Ikaros in the maintenance of the promiscuous gene profile of B-1 cells. It could be suggested that Ikaros functions as a guardian of B-1 lymphoid pattern, and that its absence directs the differentiation of B-1 cells into phagocytes.

The PGE2/IL-10 Axis Determines Susceptibility of B-1 Cell-Derived Phagocytes (B-1CDP) to Leishmania major Infection.

B-1 cells can be differentiated from B-2 cells because they are predominantly located in the peritoneal and pleural cavities and have distinct phenotypic patterns and activation properties. A mononuclear phagocyte derived from B-1 cells (B-1CDP) has been described. As the B-1CDP cells migrate to inflammatory/infectious sites and exhibit phagocytic capacity, the microbicidal ability of these cells was investigated using the Leishmania major infection model in vitro. The data obtained in this study demonstrate that B-1CDP cells are more susceptible to infection than peritoneal macrophages, since B-1CDP cells have a higher number of intracellular amastigotes forms and consequently release a larger number of promastigotes. Exacerbated infection by L. major required lipid bodies/PGE2 and IL-10 by B-1CDP cells. Both infection and the production of IL-10 were decreased when PGE2 production was blocked by NSAIDs. The involvement of IL-10 in this mechanism was confirmed, since B-1CDP cells from IL-10 KO mice are more competent to control L. major infection than cells from wild type mice. These findings further characterize the B-1CDP cells as an important mononuclear phagocyte that plays a previously unrecognized role in host responses to L. major infection, most likely via PGE2-driven production of IL-10.

B-1 cells produce insulin and abrogate experimental streptozotocin-induced diabetes.

The participation of B-1 cells in a murine model of spontaneous diabetes has been recently reported. Here, we describe the role of B-1 cells in streptozotocin (STZ) induced diabetes in mice. We demonstrated that XID (B-1 cell-deficient) mice are more susceptible to STZ treatment than WT mice, as evidenced by their higher blood glucose level in response to STZ. Unexpectedly, the XID mice that were i.p. transferred with purified B-1 cells, either before or after the STZ treatment, did not develop diabetes. These cell transfers provided long-lasting protection for the XID mice against STZ-induced diabetes, suggesting that B-1 cells play an important role in the experimental diabetes pathobiology. We also showed that B-1 cell culture supernatants were able to regulate the blood glucose level of the diabetic XID mice, and we identified insulin-producing cells when B-1 cells were differentiated in B-1 cell-derived phagocyte in vitro. These findings provide a novel role for B-1 cells in metabolic processes, presenting a new mechanism to explain the pathogenesis of diabetes and a possible therapeutical target.

Blockage of Wnt/ß-catenin signaling by quercetin reduces survival and proliferation of B-1 cells in vitro.

The Wnt/ß-catenin signaling pathway has been shown to play an important role in controlling the proliferation, survival and differentiation of hematopoietic cells. Several Wnt/ß-catenin signaling components influence hematopoietic cells fate. B-1 cells are self-renewing and spontaneously express both myeloid and lymphoid restricted transcription factors. B-1 lymphocytes play a major role in autoimmunity and are related to CD5(+) B-cell lymphomas and leukemias, such as CLL (chronic lymphocytic leukemia). Herein, we demonstrate that Wnt/ß-catenin pathway is important to B-1 cell survival in vitro. The loss of Wnt signals by quercetin treatment induces a reduction in the proliferation and survival of B-1 cells. Furthermore, the quercetin treatment diminishes IL-6 production by peritoneal cells, a cytokine important to the maintenance of B-1 cells in vitro. Importantly, the IL-6 addition to B-1 cell culture prevents cells from apoptosis, even in the presence of quercetin. These data suggest that a deregulation in ß-catenin signals could result in alterations in B-1 cell proliferation and differentiation. The correlation between Wnt/ß-catenin and IL-6 could point out a mechanism for the expansion of B-1 cells in autoimmune disease and neoplasia.

Inhibition of macrophage functions by the C-terminus of murine S100A9 is dependent on B-1 cells.

The protein S100A9 plays a key role in the control of inflammatory response. The C-terminus of the murine S100A9 protein (mS100A9p) downregulates the spreading and phagocytic activity of adherent peritoneal cells. Murine peritoneal cells are constituted by macrophages and B-1 cells, and the latter exert an inhibitory effect on macrophage functions by secreting interleukin- (IL-) 10. Here, we investigated the influence of B-1 cells on the inhibitory effect evoked by mS100A9p on macrophages. mS100A9p did not alter spreading and phagocytosis either by peritoneal macrophages obtained from mice deprived of B-1 cells or by bone marrow-derived macrophages (BMDMϕ). Nevertheless, when BMDMϕ were cocultivated by direct or indirect contact with B-1 cells treated with mS100A9p, the phagocytosis by BMDMϕ was decreased, showing that the effect of mS100A9p on macrophages was modulated by B-1 cells and/or their secretory compounds. Furthermore, the inhibitory action of mS100A9p on phagocytosis by adherent peritoneal cells was abolished in cells obtained from IL-10 knockout mice. Taken together, the results show that mS100A9p has no direct inhibitory effect on macrophages; however, mS100A9p modulates B-1 cells, which in turn downregulates macrophages, at least in part, via IL-10. These data contribute to the characterization of S100A9 functions involving B-1 cells in the regulation of the inflammatory process.

Gene expression in B-1 cells from lupus-prone mice.

New Zealand Black X New Zealand White F1 [(NZB/NZW)F1] mice develop an autoimmune condition with similarities to human systemic lupus erythematosus (SLE). In this study, we demonstrate that B-1 cells, which have previously been reported to be involved in several autoimmune diseases, have altered gene expression in these mice. RNA was extracted from purified B-1 cells of disease-free C57BL/6 mice and lupus-prone (NZB/NZW)F1 mice. Gene expression was analysed using DNA microarray techniques and validated by real time reverse transcriptase polymerase chain reaction (RT-PCR). In (NZB/NZW)F1 mice, some genes had altered expression patterns compared to disease-free controls. Specifically, the upregulation of Ifitm1, Pvrl2 and Ifi202b and downregulation of Trp53bp1 mRNA were observed in (NZB/NZW)F1 mice. These genes are known to be associated with autoimmune diseases. This pattern of gene expression in B-1 cells could understanding of the pathogenesis of SLE. Thus, it is reasonable to hypothesise that the altered gene expression observed in B-1 cells in our experimental model is important for SLE prognosis and therapy, and these implications are discussed herein.

Role of B-1 cells in the immune response against an antigen encapsulated into phosphatidylcholine-containing liposomes.

B-1 lymphocytes comprise a unique subset of B cells that differ phenotypically, ontogenetically and functionally from conventional B-2 cells. A frequent specificity of the antibody repertoire of peritoneal B-1 cells is phosphatidylcholine. Liposomes containing phosphatidylcholine have been studied as adjuvants and their interaction with dendritic cells and macrophages has been demonstrated. However, the role of B-1 cells in the adjuvanticity of liposomes composed of phosphatidylcholine has not been explored. In the present work, we studied the contribution of B-1 cells to the humoral response against ovalbumin (OVA) encapsulated into dipalmitoylphosphatidylcholine (DPPC) and cholesterol-containing liposomes. BALB/X-linked immunodeficient (xid) mice, which are deficient in B-1 cells, showed quantitative and qualitative differences in the anti-OVA antibody response compared with wild-type animals after immunization with these liposomes. The OVA-specific immune response was significantly increased in the BALB/xid mice when reconstituted with B-1 cells from naive BALB/c mice. Our results indicate the internalization of DPPC-containing liposomes by these cells and their migration from the peritoneal cavity to the spleen. Phosphatidylcholine significantly contributed to the immunogenicity of liposomes, as DPPC-containing liposomes more effectively stimulated the anti-OVA response compared with vesicles composed of dipalmitoylphosphatidylglycerol. In conclusion, we present evidence for a cognate interaction between B-1 cells and phosphatidylcholine liposomes, modulating the immune response to encapsulated antigens. This provides a novel targeting approach to assess the role of B-1 cells in humoral immunity.

Liposomes of phosphatidylcholine and cholesterol induce an M2-like macrophage phenotype reprogrammable to M1 pattern with the involvement of B-1 cells.

Macrophages respond to endogenous and non-self stimuli acquiring the M1 or M2 phenotypes, corresponding to classical or alternative activation, respectively. The role of B-1 cells in the regulation of macrophage polarization through the secretion of interleukin (IL)-10 has been demonstrated. However, the influence of B-1 cells on macrophage phenotype induction by an immunogen that suppress their ability to secrete IL-10 has not been explored. Here, we studied the peritoneal macrophage pattern induced by liposomes comprised of dipalmitoylphosphatidylcholine (DPPC) and cholesterol (Chol) carrying ovalbumin (OVA) (Lp DPPC/OVA), and the involvement of B-1 cells in macrophage polarization. Peritoneal cells from BALB/c, B-1 cells-deficient BALB/xid and C57BL/6 mice immunized with Lp DPPC/OVA and OVA in soluble form (PBS/OVA) were analyzed and stimulated or not in vitro with lipopolysaccharide (LPS). Peritoneal macrophages from BALB/c and C57BL/6 mice immunized with Lp DPPC/OVA showed an M2-like phenotype as evidenced by their high arginase activity without LPS stimulation. Upon stimulation, these macrophages were reprogrammable toward the M1 phenotype with the upregulation of nitric oxide (NO) and a decrease in IL-10 secretion. In addition, high IFN-γ levels were detected in the culture supernatant of peritoneal cells from BALB/c and C57BL/6 mice immunized with Lp DPPC/OVA. Nevertheless, still high levels of arginase activity and undetectable levels of IL-12 were found, indicating that the switch to a classical activation state was not complete. In the peritoneal cells from liposomes-immunized BALB/xid mice, levels of arginase activity, NO, and IL-6 were below those from wild type animals, but the last two products were restored upon adoptive transfer of B-1 cells, together with an increase in IFN-γ secretion. Summarizing, we have demonstrated that Lp DPPC/OVA induce an M2-like pattern in peritoneal macrophages reprogrammable to M1 phenotype after LPS stimulation, with the involvement of B-1 cells.