Regulatory B cells present in lymph nodes draining a murine tumor.

In cancer, B cells have been classically associated with antibody secretion, antigen presentation and T cell activation. However, a possible role for B lymphocytes in impairing antitumor response and collaborating with tumor growth has been brought into focus. Recent reports have described the capacity of B cells to negatively affect immune responses in autoimmune diseases. The highly immunogenic mouse tumor MCC loses its immunogenicity and induces systemic immune suppression and tolerance as it grows. We have previously demonstrated that MCC growth induces a distinct and progressive increase in B cell number and proportion in the tumor draining lymph nodes (TDLN), as well as a less prominent increase in T regulatory cells. The aim of this research was to study B cell characteristics and function in the lymph node draining MCC tumor and to analyze whether these cells may be playing a role in suppressing antitumor response and favoring tumor progression. Results indicate that B cells from TDLN expressed increased CD86 and MHCII co-stimulatory molecules indicating activated phenotype, as well as intracellular IL-10, FASL and Granzyme B, molecules with regulatory immunosuppressive properties. Additionally, B cells showed high inhibitory upon T cell proliferation ex vivo, and a mild capacity to secrete antibodies. Our conclusion is that even when evidence of B cell-mediated activity of the immune response is present, B cells from TDLN exhibit regulatory phenotype and inhibitory activity, probably contributing to the state of immunological tolerance characteristic of the advanced tumor condition.

Lymphadenectomy exacerbates tumor growth while lymphadenectomy plus the adoptive transfer of autologous cytotoxic cells and low-dose cyclophosphamide induces regression of an established murine fibrosarcoma.

Tumor-draining lymph node (TDLN) ablation is routinely performed in the management of cancer; nevertheless, its usefulness is at present a matter of debate. TDLN are central sites where T cell priming to tumor antigens and onset of the antitumor immune response occur. However, tumor-induced immunosuppression has been demonstrated at TDLN, leading to downregulation of antitumor reaction and tolerance induction. Tolerance in turn is a main impairment for immunotherapy trials. We used a murine immunogenic fibrosarcoma that evolves to a tolerogenic state, to study the cellular and molecular mechanisms underlying tolerance induction at the level of TDLN and to design an appropriate immunotherapy. We determined that following a transient activation, the established tumor induces signs of immunosuppression at TDLN that coexist with local and systemic evidences of antitumor response. Therefore, we evaluated the feasibility of removing TDLN in order to eliminate a focus of immunosuppression and favor tumor rejection; but instead, a marked exacerbation of tumor growth was induced. Combining TDLN ablation with the in vivo depletion of regulatory cells by low-dose cyclophosphamide and the restoring of the TDLN-derived cells into the donor mouse by adoptive transference, resulted in lowered tumor growth, enhanced survival and a considerable degree of tumor regression. Our results demonstrate that important antitumor elements can be eliminated by lymphadenectomy and proved that the concurrent administration of low-dose chemotherapy along with the reinoculation of autologous cytotoxic cells provides protection. We suggest that this protocol may be useful, especially in the cases where lymphadenectomy is mandatory.

B cells inhibit the antitumor immunity against an established murine fibrosarcoma.

Despite the classic role of B cells in favoring the immune response, an inhibitory action of B lymphocytes in tumor immunity has emerged in certain studies. In methylcolanthrene-induced murine fibrosarcoma (MCC), the loss of immunogenicity and the establishment of tolerance are paralleled by systemic immune suppression and the appearance of B+IL-10+ cells in tumor-draining lymph nodes. The present study aimed to assess the role of the B+IL-10+ cell population in the immune evasion and tolerance induced by MCC through the depletion of B cells in mice at various times of tumor progression: Prior to or subsequent to tumor implantation. Tumor growth and immunological parameters were evaluated. B cell depletion prior to tumor inoculum enhanced tumor growth, initiating the onset of the tumor-induced systemic immune response; however, an increase in the T regulatory cells (Tregs) at the tumor-draining lymph node could account for tumor exacerbation. B cell depletion once the tumor was established resulted in decreased tumor growth and a delayed onset of tolerance. Additionally, B cell absence exacerbated T cell dependent-tumor rejection, reduced Tregs and increased cytotoxic CD8+ T cells. In vitro analysis showed a direct effect of B cells upon T cell proliferation. In conclusion, B cell depletion exerts opposite effects when performed prior to or subsequent to tumor implantation. In this initially immunogenic tumor, B cell absence would delay the establishment of immunological tolerance probably by unmasking a pre-existing antitumor response. The present findings elucidate the convenience of modulating B cells in the development of future and more effective immunotherapies against cancer.

Differential expression of function-related antigens on blood monocytes in children with hemolytic uremic syndrome.

Monocytes (Mo) mediate central functions in inflammation and immunity. Different subpopulations of Mo with distinct phenotype and functional properties have been described. Here, we investigate the phenotype and function of peripheral Mo from children with hemolytic uremic syndrome (HUS). For this purpose, blood samples from patients in the acute period of HUS (HUS AP) were obtained on admission before dialysis and/or transfusion. The Mo phenotypic characterization was performed on whole blood by flow cytometry, and markers associated to biological functions were selected: CD14 accounting for lipopolysaccharide (LPS) responsiveness, CD11b for adhesion, Fc receptor for immunoglobulin G type I (FcgammaRI)/CD64 for phagocytosis and cytotoxicity, and human leukocyte antigen (HLA)-DR for antigen presentation. Some of these functions were also determined. Moreover, the percentage of CD14+ CD16+ Mo was evaluated. We found that the entire HUS AP Mo population exhibited reduced CD14, CD64, and CD11b expression and decreased LPS-induced tumor necrosis factor production and Fcgamma-dependent cytotoxicity. HUS AP showed an increased percentage of CD14+ CD16+ Mo with higher CD16 and lower CD14 levels compared with the same subset from healthy children. Moreover, the CD14++ CD16- Mo subpopulation of HUS AP had a decreased HLA-DR expression, which correlated with severity. In conclusion, the Mo population from HUS AP patients presents phenotypic and functional alterations. The contribution to the pathogenesis and the possible scenarios that led to these changes are discussed.

[Activation of innate and specific immune responses in hemolytic uremic syndrome (HUS)-patients]. / Activación de la respuesta inmune innata y específica en los pacientes con síndrome urémico hemolítico. Papel dual a traves de la participacion en los mecanismos patogenicos y protectores.

The central role of the immune system is the preservation of the health against several pathogenic microbes and injury agents. However, on special conditions defensive mechanisms triggered towards the foreign agent can damage the host. Clinical and experimental evidence indicate that inflammatory reaction triggered by the main components of Shiga toxin (Stx)-producing Escherichia coil (STEC), participate in the evolution to the complete form of HUS. When children are diagnosed of HUS, they present evidence that have suffered a very strong and early inflammatory response. These features include: the presence of a marked neutrophilia, the polymorfonuclear leucocytes (PMN) are "deactivated or exhausted" and the monocytes are differentiated towards an inflammatory phenotype (CD14-reduced and CD16-enhanced membrane expression). In addition, HUS-patients show a marked reduction in the absolute and relative number of leucocytes carrying the receptor (CX3CR1) for the chemokine "Fractalkine" (FKN, CX3CL1), which are the classic monocytes and Natural Killer cells (NK). All these cells express a high cytotoxic potencial. The chemokine FKN is expressed in endothelial and epithelial renal cells, and is involved in the pathogenic mechanism of different nephropathies. Noteworthy, we found a significant correlation between the severity of the renal damage (as days of anuria) and the alterations described above. Finally, the protective role of specific immune response, mainly through the antibody production with Stx-neutralizing capacity, is discussed.

Regulatory cells induced by acute toxoplasmosis prevent the development of allergic lung inflammation.

The increased prevalence of allergies in developed countries has been attributed to a reduction of some infections. Supporting epidemiological studies, we previously showed that both acute and chronic Toxoplasma gondii infection can diminish allergic airway inflammation in BALB/c mice. The mechanisms involved when sensitization occurs during acute phase would be related to the strong Th1 response induced by the parasite. Here, we further investigated the mechanisms involved in T. gondii allergy protection in mice sensitized during acute T. gondii infection. Adoptive transference assays and ex vivo co-cultures experiments showed that not only thoracic lymph node cells from infected and sensitized mice but also from non-sensitized infected animals diminished both allergic lung inflammation and the proliferation of effector T cells from allergic mice. This ability was found to be contact-independent and correlated with high levels of CD4(+)FoxP3(+) cells. IL-10 would not be involved in allergy suppression since IL-10-deficient mice behaved similar to wild type mice. Our results extend earlier work and show that, in addition to immune deviation, acute T. gondii infection can suppress allergic airway inflammation through immune suppression.

Regulatory B cells present in lymph nodes draining a murine tumor

In cancer, B cells have been classically associated with antibody secretion, antigen presentation and T cell activation. However, a possible role for B lymphocytes in impairing antitumor response and collaborating with tumor growth has been brought into focus. Recent reports have described the capacity of B cells to negatively affect immune responses in autoimmune diseases. The highly immunogenic mouse tumor MCC loses its immunogenicity and induces systemic immune suppression and tolerance as it grows. We have previously demonstrated that MCC growth induces a distinct and progressive increase in B cell number and proportion in the tumor draining lymph nodes (TDLN), as well as a less prominent increase in T regulatory cells. The aim of this research was to study B cell characteristics and function in the lymph node draining MCC tumor and to analyze whether these cells may be playing a role in suppressing antitumor response and favoring tumor progression. Results indicate that B cells from TDLN expressed increased CD86 and MHCII co-stimulatory molecules indicating activated phenotype, as well as intracellular IL-10, FASL and Granzyme B, molecules with regulatory immunosuppressive properties. Additionally, B cells showed high inhibitory upon T cell proliferation ex vivo, and a mild capacity to secrete antibodies. Our conclusion is that even when evidence of B cell-mediated activity of the immune response is present, B cells from TDLN exhibit regulatory phenotype and inhibitory activity, probably contributing to the state of immunological tolerance characteristic of the advanced tumor condition.

Anti-inflammatory pretreatment enables an efficient dendritic cell-based immunotherapy against established tumors.

Although animals can be immunized against the growth of some tumor implants, most of the attempts to use immunotherapy to cause the regression of animal and human tumors once they have become established have been disappointing even when strongly immunogenic tumors were used as target. In this paper, we demonstrate that the failure to achieve an efficient immunological treatment against an established strongly immunogenic murine fibrosarcoma was paralleled with the emergence of a state of immunological unresponsiveness (immunological eclipse) against tumor antigens observed when the tumor surpassed the critical size of 500 mm(3). In turn, the onset of the immunological eclipse was coincidental with the onset of a systemic inflammatory condition characterized by a high number of circulating and splenic polymorphonucleated neutrophils (PMN) displaying activation and Gr1(+)Mac1(+) phenotype and an increasing serum concentration of the pro-inflammatory cytokines TNF-alpha, IL-1beta and IL-6 cytokines and C-reactive protein (CRP) and serum A amyloid (SAA) phase acute proteins. Treatment of tumor-bearing mice with a single low dose (0.75 mg/kg) of the synthetic corticoid dexamethasone (DX) significantly reduced all the systemic inflammatory parameters and simultaneously reversed the immunological eclipse, as evidenced by the restoration of specific T-cell-dependent concomitant immunity, ability of spleen cells to transfer anti-tumor activity and recovery of T-cell signal transduction molecules. Two other anti-inflammatory treatments by using indomethacin or dimeric TNF-alpha receptor, also partially reversed the immunological eclipse although the effect was not as striking as that observed with DX. The reversion of the immunological eclipse was not enough on its own to inhibit the primary growing tumor. However, when we used the two-step strategy of inoculating DX to reverse the eclipse and then dendritic cells loaded with tumor antigens (DC) as an immunization booster, a significant inhibition of the growth of both established tumors and remnant tumor cells after excision of large established tumors was observed, despite the fact that the vaccination alone (DC) had no effect or even enhanced tumor growth in certain circumstances. The two-step strategy of tumor immunotherapy that we present is based on the rationale that it is necessary to eliminate or ameliorate the immunological eclipse as a precondition to allow an otherwise ineffective anti-tumor immunological therapy to have a chance to be successful.

Protective role of nitric oxide in mice with Shiga toxin-induced hemolytic uremic syndrome.

BACKGROUND: Nitric oxide (NO) is an endogenous vasodilator and platelet inhibitor. An enhanced NO production has been detected in patients with hemolytic uremic syndrome (HUS), although its implication in HUS pathogenesis has not been clarified. METHODS: A mouse model of Shiga toxin 2 (Stx2)-induced HUS was used to study the role of NO in the development of the disease. Modulation of l-arginine-NO pathway was achieved by oral administration of NO synthase (NOS) substrate or inhibitors, and renal damage, mortality and platelet activity were evaluated. The involvement of platelets was studied by means of a specific anti-platelet antibody. RESULTS: Inhibition of NO generation by the NOS inhibitor L-NAME enhanced Stx2-mediated renal damage and lethality; this effect was prevented by the addition of l-arginine. The worsening effect of L-NAME involved enhanced Stx2-mediated platelet activation, and it was completely prevented by platelet depletion. CONCLUSIONS: NO exerts a protective role in the early pathogenesis of HUS, and its inhibition potentiates renal damage and mortality through a mechanism involving enhanced platelet activation.