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.

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.

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.

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

B-cell lymphopoiesis is regulated by cathepsin L.

Cathepsin L (CTSL) is a ubiquitously expressed lysosomal cysteine peptidase with diverse and highly specific functions. The involvement of CTSL in thymic CD4+ T-cell positive selection has been well documented. Using CTSL(nkt/nkt) mice that lack CTSL activity, we have previously demonstrated that the absence of CTSL activity affects the homeostasis of the T-cell pool by decreasing CD4+ cell thymic production and increasing CD8+ thymocyte production. Herein we investigated the influence of CTSL activity on the homeostasis of peripheral B-cell populations and bone marrow (BM) B-cell maturation. B-cell numbers were increased in lymph nodes (LN), spleen and blood from CTSL (nkt/nkt) mice. Increases in splenic B-cell numbers were restricted to transitional T1 and T2 cells and to the marginal zone (MZ) cell subpopulation. No alterations in the proliferative or apoptosis levels were detected in peripheral B-cell populations from CTSL (nkt/nkt) mice. In the BM, the percentage and the absolute number of pre-pro-B, pro-B, pre-B, immature and mature B cells were not altered. However, in vitro and in vivo experiments showed that BM B-cell production was markedly increased in CTSL (nkt/nkt) mice. Besides, BM B-cell emigration to the spleen was increased in CTSL (nkt/nkt) mice. Colony-forming unit pre-B (CFU pre-B) assays in the presence of BM stromal cells (SC) and reciprocal BM chimeras revealed that both BM B-cell precursors and SC would contribute to sustain the increased B-cell hematopoiesis in CTSL (nkt/nkt) mice. Overall, our data clearly demonstrate that CTSL negatively regulates BM B-cell production and output therefore influencing the homeostasis of peripheral B cells.

[Increase of regulatory T cells in the lymph node of cathepsin L mutant mice]. / Aumento de linfocitos T regulatorios en los ganglios linfoides de ratones mutantes para catepsina L.

Regulatory CD4+CD25+Foxp3+ T cells (Treg) have been implicated in different pathologies including cancer, infections and autoimmune diseases and in the rejection of allogeneic organ transplantation. Thus, modulation of Treg activity has a great potential in the treatment of these pathologies. Herein, we evaluated the influence of cathepsin L (CTSL) on Treg homeostasis. CTSL mutant mice (CTSLnkt/nkt) showed a decrease in the absolute number of thymic Treg cells. In contrast, the absolute number of lymph node Treg cells and their frequency within CD4+ cells were increased. The absence of CTSL activity in CD4+ T cells -and not in their environment- increased the proliferation rate of lymph node CD4+ T cells. Treg and T CD4+ conventional (CD4+CD25-Foxp3-) cells from mutant mice showed similar increases in their proliferative levels as compared with control mice, suggesting that although proliferation contributes to the increases in their number, the augmentation in the frequency of Treg cells is not only associated to increases in proliferation. Furthermore, the Treg apoptosis rate was not decreased in the lymph node of CTSLnkt/nkt mice. Taking into account that the daily CD4+ thymic production is diminished in mutant mice, our results suggest that peripheral Treg increases are probably not the result of increased thymic output and raise the possibility that a conversion to Treg phenotype would be favored in the CD4+ T cells peripheral pool of CTSL mutant mice.

[Regulatory T cell depletion increases the number of CD8 cells during mouse mammary tumor virus infection]. / La depleción de las células T regulatorias aumenta el número de las células CD8 durante la infección con el virus del tumor mamario murino.

Mouse mammary tumor virus (MMTV) is a milk-borne betaretrovirus that has developed strategies to exploit and subvert the host immune system. We have shown in a natural model of MMTV infection that the virus causes early and progressive increases in superantigen (Sag)-specific CD4+ CD25+ Foxp3+ regulatory T cells (Treg) in Peyer's patches. Herein, we evaluated whether the depletion of Treg cells affects the CD8+ population during milk-borne MMTV infection. At day 6 of infection, the depletion of Treg cells increased the percentage and absolute number of CD8+ cells in lymph nodes as well as the mean intensity fluorescence of the CD44 activation marker. The absolute number of CD8+ cells was increased in cells bearing both Sag reactive and non-reactive TCR Vß chains. We have previously shown that regulatory T cell depletion at day 6 of infection decrease viral load. Results reported herein suggest that at least after day 6 of MMTV infection Treg cells play an inhibiting role on CD8 antiviral response.

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.

Avaliação in vitro, in vivo e pelo método dos elementos finitos da expansão palatal implantossuportada / In vitro, in vivo and finite element method evaluation of implantsupported palatal expansion

A expansão palatal implantossuportada (Epis) permite a abertura da sutura palatina evitando os efeitos indesejáveis da expansão maxilar sobre as estruturas dentoalveolares. Os aparelhos da técnica Epis são ancorados por dois implantes inseridos próximos à sutura palatina mediana. Métodos: este estudo foi conduzido em três estágios: aparelhos Epis foram instalados e ativados em dois crânios humanos adultos para avaliação das deformações ósseas craniofaciais através de extensometria com strain gauges; foram criados tridimensionalmente (3D) um modelo do complexo nasomaxilar e um aparelho Epis os quais foram unidos e receberam propriedades físicas e condições de contorno apropriadas para análisepelo método dos elementos finitos (MEF); foi realizada avaliação clínica de dois aparelhos instalados em pacientes adultos com necessidade de expansão maxilar. Os resultados dos strain gauges validaram qualitativamente os resultados do MEF pela coincidência dos locaiscom tensões trativas e compressivas nos modelos 3D mostrando o bom desempenho biomecânico da expansão palatal com aparelhos Epis. Estes locais também correspondem às áreas clinicamente consideradas como de alta resistência à expansão maxilar. A avaliação in vivo mostrou a facilidade de instalação e remoção do aparelho. Conclusão: a expansão palatal implantossuportada pode ser empregada com ou sem auxílio cirúrgico, dependendo da resistência óssea, sendo sua principal indicação na constrição maxilar com poucos dentesposteriores para ancoragem ou com limitações periodontais.

The implant supported palatal expander (Epis) was developed to eliminatethe undesirable effects on dentoalveolar structures due to upper jaw expansion. The Epis devices are anchored by two implants placed near the mid palatal suture. Methods: this study was conducted on three steps: Eois were installed and activated in two human adult skulls for assessment of craniofacial bane deformations by strain gauges, a naso-maxillary modeland an Epis model were tridimensionally (3D) created, assembled and received physical properties and boundary conditions suitable for finite element methods (MEF) and clinical evaluation was carried out by installing Eois appliances in two adult patients in need of upper jaw expansion. Results: the strain gauges results qualitatively validated the MEF results on3D models by the coincidence of the sites with compressive and tensile stress showing the good biomechanics performance of the palatal expansion with Eois devices. Those sites alsocorrespond to the upper jaw areas considered clinically as high resistance to expansion. In vivo evaluation proves the facility to install and remove the device. Conclusions: the implantsupported palatal expansion can be employed with ar without surgical assistance, depends on bane resistance being its main indication in upper jaw constriction with few posterior teethfor anchor ar with periodontallimitations.

Increases in IgA(+) B cells in Peyer's patches during milk-borne mouse mammary tumor virus infection are influenced by Toll-like receptor 4 and are completely dependent on the superantigen response.

Mouse mammary tumor virus (MMTV) is a milk-borne betaretrovirus that has developed strategies to exploit and subvert the host immune system. Although mammary glands are the final target of infection, Peyer's patches (PP) are the entry site of the virus. Herein, we show that the infection induces increases in the number of PP IgA(+) B cells and higher expression of the α circular transcript, which is a specific marker of the switch to IgA. In addition, IgA(+) B-cell increases correlated with higher levels of cytokines related to IgA class switching, such as interleukin (IL)-5 and IL-6. Of interest, the increases in IgA(+) B cells were lower in Toll-like receptor 4-deficient mice and were completely dependent on the presence of superantigen-reactive T cells. Our results point to a novel mechanism involved in MMTV infection and suggest that IgA(+) B cells may play an important role in carrying the virus to the mammary glands.

Mouse bone marrow-derived mesenchymal stromal cells turn activated macrophages into a regulatory-like profile.

In recent years it has become clear that the therapeutic properties of bone marrow-derived mesenchymal stromal cells (MSC) are related not only to their ability to differentiate into different lineages but also to their capacity to suppress the immune response. We here studied the influence of MSC on macrophage function. Using mouse thioglycolate-elicited peritoneal macrophages (M) stimulated with LPS, we found that MSC markedly suppressed the production of the inflammatory cytokines TNF-alpha, IL-6, IL-12p70 and interferon-gamma while increased the production of IL-10 and IL-12p40. Similar results were observed using supernatants from MSC suggesting that factor(s) constitutively released by MSC are involved. Supporting a role for PGE(2) we observed that acetylsalicylic acid impaired the ability of MSC to inhibit the production of inflammatory cytokines and to stimulate the production of IL-10 by LPS-stimulated M. Moreover, we found that MSC constitutively produce PGE2 at levels able to inhibit the production of TNF-alpha and IL-6 by activated M. MSC also inhibited the up-regulation of CD86 and MHC class II in LPS-stimulated M impairing their ability to activate antigen-specific T CD4+ cells. On the other hand, they stimulated the uptake of apoptotic thymocytes by M. Of note, MSC turned M into cells highly susceptible to infection with the parasite Trypanosoma cruzi increasing more than 5-fold the rate of M infection. Using a model of inflammation triggered by s.c. implantation of glass cylinders, we found that MSC stimulated the recruitment of macrophages which showed a low expression of CD86 and the MHC class II molecule Ia(b) and a high ability to produce IL-10 and IL-12p40, but not IL-12 p70. In summary, our results suggest that MSC switch M into a regulatory profile characterized by a low ability to produce inflammatory cytokines, a high ability to phagocyte apoptotic cells, and a marked increase in their susceptibility to infection by intracellular pathogens.

Early increases in superantigen-specific Foxp3+ regulatory T cells during mouse mammary tumor virus infection.

Mouse mammary tumor virus (MMTV) is a milk-borne betaretrovirus that has developed strategies to exploit and subvert the host immune system. Here, we show in a natural model of MMTV infection that the virus causes early and progressive increases in superantigen (SAg)-specific Foxp3(+) regulatory T cells (T(reg)) in Peyer's patches (PP). These increases were shown to be dependent on the presence of dendritic cells. CD4(+) CD25(+) T cells from the PP of infected mice preferentially suppress the proliferative response of T cells to SAg-expressing antigen-presenting cells ex vivo. We investigated the influence of the depletion of CD25(+) cells at different stages of the infection. When CD25(+) cells were depleted before MMTV infection, an increase in the number of PP SAg-cognate Foxp3(-) T cells was found at day 6 of infection. Since the SAg response is associated with viral amplification, the possibility exists that T(reg) cells attenuate the increase in viral load at the beginning of the infection. In contrast, depletion of CD25(+) cells once the initial SAg response has developed caused a lower viral load, suggesting that at later stages T(reg) cells may favor viral persistence. Thus, our results indicated that T(reg) cells play an important and complex role during MMTV infection.

Precisión del certificado de defunción comparado con la autopsia verbal: estudio PRISMA / Accuracy of the death certificate (DC) to assess the cause of death and comparison with the verbal autopsy: the PRISMA study

Los datos del certificado de defunción no reflejan ajustadamente las causas y las circunstancias de la muerte. La comparación con otros métodos de información, como la autopsia verbal, podría demostrar las falencias de los registros. Objetivos: 1. Identificar las causas de muerte en 20 ciudades argentinas mediante la autopsia verbal y compararlas con las que constan en el certificado de defunción. 2. Analizar la muerte cardiovascular en cuanto a antecedentes y factores de riesgo. Material y métodos: Se incluyeron todos los mayores de 18 años fallecidos durante 2 meses del año 2004 en las ciudades participantes. Resultados: Se constataron 1274 muertes. Según la autopsia verbal, las causas de muerte cardiovascular más frecuentes fueron insuficiencia cardíaca (23 por ciento), accidente cerebrovascular (11,3 por ciento) e infarto de miocardio (8 por ciento) y las no cardiovasculares fueron neoplasias (21,5 por cierto), neumopatías (7,6 por ciento) e infecciones (6,6 por ciento). En el 11,7 por ciento de los fallecidos no se pudo establecer claramente la causa de muerte según el certificado.La concordancia de ambos métodos para definir la causa de muerte según el coeficiente V de Cramer fue de 0,608, el valor de kappa fue de 0,614 (0,580-0,647) y el de kappa ponderado fue de 0,596 (0,555-0,637). Existió un subregistro del 9,7 por ciento de insuficiencia cardíaca según el certificado y un sobrerregistro del 6,4 por ciento en muerte por otras causas cardiovasculares conrespecto a la autopsia verbal. Los fallecidos de causa cardiovascular presentaron con más frecuencia factores de riesgo y antecedentes cardiovasculares. Conclusiones: En un porcentaje elevado de certificados de defunción no se pudo establecer claramente la causa de muerte. La mayor discordancia se registró en la muerte por insuficiencia cardíaca y otras causas cardiovasculares.

Precisión del certificado de defunción comparado con la autopsia verbal: estudio PRISMA / Accuracy of the death certificate (DC) to assess the cause of death and comparison with the verbal autopsy: the PRISMA study

Los datos del certificado de defunción no reflejan ajustadamente las causas y las circunstancias de la muerte. La comparación con otros métodos de información, como la autopsia verbal, podría demostrar las falencias de los registros. Objetivos: 1. Identificar las causas de muerte en 20 ciudades argentinas mediante la autopsia verbal y compararlas con las que constan en el certificado de defunción. 2. Analizar la muerte cardiovascular en cuanto a antecedentes y factores de riesgo. Material y métodos: Se incluyeron todos los mayores de 18 años fallecidos durante 2 meses del año 2004 en las ciudades participantes. Resultados: Se constataron 1274 muertes. Según la autopsia verbal, las causas de muerte cardiovascular más frecuentes fueron insuficiencia cardíaca (23 por ciento), accidente cerebrovascular (11,3 por ciento) e infarto de miocardio (8 por ciento) y las no cardiovasculares fueron neoplasias (21,5 por cierto), neumopatías (7,6 por ciento) e infecciones (6,6 por ciento). En el 11,7 por ciento de los fallecidos no se pudo establecer claramente la causa de muerte según el certificado.La concordancia de ambos métodos para definir la causa de muerte según el coeficiente V de Cramer fue de 0,608, el valor de kappa fue de 0,614 (0,580-0,647) y el de kappa ponderado fue de 0,596 (0,555-0,637). Existió un subregistro del 9,7 por ciento de insuficiencia cardíaca según el certificado y un sobrerregistro del 6,4 por ciento en muerte por otras causas cardiovasculares conrespecto a la autopsia verbal. Los fallecidos de causa cardiovascular presentaron con más frecuencia factores de riesgo y antecedentes cardiovasculares. Conclusiones: En un porcentaje elevado de certificados de defunción no se pudo establecer claramente la causa de muerte. La mayor discordancia se registró en la muerte por insuficiencia cardíaca y otras causas cardiovasculares. (AU)

Precisión del certificado de defunción comparado con la autopsia verbal: estudio PRISMA / Accuracy of the death certificate (DC) to assess the cause of death and comparison with the verbal autopsy: the PRISMA study

Los datos del certificado de defunción no reflejan ajustadamente las causas y las circunstancias de la muerte. La comparación con otros métodos de información, como la autopsia verbal, podría demostrar las falencias de los registros. Objetivos: 1. Identificar las causas de muerte en 20 ciudades argentinas mediante la autopsia verbal y compararlas con las que constan en el certificado de defunción. 2. Analizar la muerte cardiovascular en cuanto a antecedentes y factores de riesgo. Material y métodos: Se incluyeron todos los mayores de 18 años fallecidos durante 2 meses del año 2004 en las ciudades participantes. Resultados: Se constataron 1274 muertes. Según la autopsia verbal, las causas de muerte cardiovascular más frecuentes fueron insuficiencia cardíaca (23 por ciento), accidente cerebrovascular (11,3 por ciento) e infarto de miocardio (8 por ciento) y las no cardiovasculares fueron neoplasias (21,5 por cierto), neumopatías (7,6 por ciento) e infecciones (6,6 por ciento). En el 11,7 por ciento de los fallecidos no se pudo establecer claramente la causa de muerte según el certificado.La concordancia de ambos métodos para definir la causa de muerte según el coeficiente V de Cramer fue de 0,608, el valor de kappa fue de 0,614 (0,580-0,647) y el de kappa ponderado fue de 0,596 (0,555-0,637). Existió un subregistro del 9,7 por ciento de insuficiencia cardíaca según el certificado y un sobrerregistro del 6,4 por ciento en muerte por otras causas cardiovasculares conrespecto a la autopsia verbal. Los fallecidos de causa cardiovascular presentaron con más frecuencia factores de riesgo y antecedentes cardiovasculares. Conclusiones: En un porcentaje elevado de certificados de defunción no se pudo establecer claramente la causa de muerte. La mayor discordancia se registró en la muerte por insuficiencia cardíaca y otras causas cardiovasculares. (AU)

Tumor transition zone: a putative new morphological and functional hallmark of tumor aggressiveness.

A small primary or secondary tumor load can occasionally induce more deleterious effects than a histologically identical larger one. In the four murine models studied herein this enhanced tumor aggressiveness could not be attributed to NRAS mutations or other hereditary changes, differential vascularization of live tumor tissues, or necrosis content. Instead, the main tumor feature associated with a more aggressive behavior was the presence of a high number of vessels, sometimes filled with inflammatory cells, inside a tumor area, which we have identified and designated as the transition zone between the live and the necrotic zones. Our experiments suggest that during tumor growth, different cachectic factors are produced within the transition and necrotic zones by dying tumor cells and by tumor infiltrating macrophages only reaching the general circulation through the vessels present in the transition zone. Therefore, a small tumor displaying high vascularization of its transition area could be harmful to its host, while, in contrast, a large tumor could behave as a relatively benign one if its transition zone exhibited little or no vascularization, and in consequence its cachectic factors remained "trapped." Similar histological images to those observed in mice were seen in a significant percentage of human cancer biopsies, raising the possibility that such images might have a prognostic value.

Cathepsin-L influences the expression of extracellular matrix in lymphoid organs and plays a role in the regulation of thymic output and of peripheral T cell number.

Nackt mice, which are deficient in cathepsin-L (CTSL), show an early impairment during positive selection in the context of class II MHC molecules and as a consequence, the percentage and absolute number of CD4(+) thymocytes are significantly decreased. In this study, we show that lymph nodes from nackt mice are hypertrophied, showing normal absolute numbers of CD4(+) T cells and marked increases in the number of CD8(+) T lymphocytes. Basal proliferative levels are increased in the CD4(+) but not in the CD8(+) population. Lymph node T cells show increases in the expression of alpha(5), alpha(6), and beta(1) integrin chains. These alterations correlate with increases in the expression of extracellular matrix (ECM) components in lymph nodes. Interestingly, laminin, fibronectin, and collagen I and IV are markedly decreased in nackt thymus which shows an augmented output of CD8(+) cells. These results demonstrate that a mutation in the Ctsl gene influences the levels of ECM components in lymphoid organs, the thymic output, and the number of T cells in the periphery. They further raise the possibility that, by regulating the level of expression of ECM components in lymphoid organs, CTSL is able to broadly affect the immune system.