Splenic Transcriptional Responses in Severe Visceral Leishmaniasis: Impaired Leukocyte Chemotaxis and Cell Cycle Arrest.

Structural changes in the spleen have been reported in several infectious diseases. In visceral leishmaniasis (VL), a severe parasitic disease caused by Leishmania spp., the loss of white pulp accompanies a severe clinical presentation. Hamster model reproduces aspects of human VL progression. In the early stages, a transcriptomic signature of leukocyte recruitment was associated with white pulp hyperplasia. Subsequently, impaired leukocyte chemotaxis with loss of T lymphocytes in the periarteriolar lymphoid sheath occurred. This differential gene expression was subsequently corroborated by transcriptomic profiling of spleens in severe human VL. At the latest stage, spleen disorganization was associated with increasing clinical signs of VL. White pulp disruption was accompanied by decreased DLK1 expression. The expression of CXCL13, CCR5, CCL19, CCR6, CCR7 and LTA decreased, likely regulated by CDKN2A overexpression. Our findings enlighten a pathway implying cell cycle arrest and decreased gene expression involved in spleen organization.

Phenotypical Characterization of Spleen Remodeling in Murine Experimental Visceral Leishmaniasis.

Background: Visceral leishmaniasis (VL) is caused by Leishmania infantum or L. donovani infection. One of the main problems related to this disease is the emergence of severe clinical forms with a lethality of 5-20%, even while under specific treatment. In humans and other species susceptible to fatal VL, such as dogs and hamsters, the disruption of splenic white pulp (WP) is accompanied by disease progression. Control of VL progression is seen in BALB/c mice, as evidenced by a mild clinical presentation and controlled parasite replication in the liver and spleen. In this study, we investigated the features involved in the morphological remodeling of splenic compartments associated with the control of VL progression to death. Methods: We evaluated cohorts of BALB/c mice after 30, 60, and 90 days of infection by L. infantum. Spleen morphology, cell population subsets and cytokine production were studied in the spleen using flow- and histo-cytometry. Results: Intraperitoneal infection with 108 promastigotes of L. infantum led to progressive increases in spleen size at 60 and 90 days after infection. Splenomegaly was the only clinical sign of disease observed. At 30 days after infection, hyperplasia in the WP and decreased numbers of plasmacytoid dendritic cells were observed. The WP hyperplasia subsided at 60 days post-infection. However, the splenomegaly remained in association with increased numbers of macrophages, B and T lymphocytes and plasma cells. An increased number of lymphoid tissue inducer (LTi) cells was observed; these were distributed around the periarteriolar lymphoid sheath in control mice and scattered throughout the red pulp in the Leishmania-infected mice. After 90 days of infection, increased IL-6 and IFN-γ production was seen in the spleen, as well as higher frequencies of follicular and plasmacytoid dendritic cells. Conclusion: The data presented herein emphasizes the potential role of spleen remodeling in the control of severe forms of VL and highlights features potentially involved in this process.

Histological Disorganization of Spleen Compartments and Severe Visceral Leishmaniasis.

The spleen is a secondary lymphoid organ responsible for immune surveillance against blood-circulating pathogens. Absence of the spleen is associated with increased susceptibility to systemic spread and fatal infection by different pathogens. Severe forms of visceral leishmaniasis are associated with disorganization of spleen compartments where cell interactions essential for splenic immunological function take place. White pulp atrophies, secondary lymphoid follicles and marginal zones vanish, and the boundaries separating white and red pulp blur. Leukocyte populations are reduced or disappear or are replaced by plasma cells. In this paper, we review the published data on spleen disorganization in severe forms of visceral leishmaniasis and propose a histological classification to help the exchange of information among research groups.

Leishmania infection modulates beta-1 integrin activation and alters the kinetics of monocyte spreading over fibronectin.

Contact with Leishmania leads to a decreases in mononuclear phagocyte adherence to connective tissue. In this work, we studied the early stages of bond formation between VLA4 and fibronectin, measured the kinetics of membrane alignment and the monocyte cytoplasm spreading area over a fibronectin-coated surface, and studied the expression of high affinity integrin epitope in uninfected and Leishmania-infected human monocytes. Our results show that the initial VLA4-mediated interaction of Leishmania-infected monocyte with a fibronectin-coated surface is preserved, however, the later stage, leukocyte spreading over the substrate is abrogated in Leishmania-infected cells. The median of spreading area was 72 [55-89] µm(2) for uninfected and 41 [34-51] µm(2) for Leishmania-infected monocyte. This cytoplasm spread was inhibited using an anti-VLA4 blocking antibody. After the initial contact with the fibronectrin-coated surface, uninfected monocyte quickly spread the cytoplasm at a 15 µm(2) s(-1) ratio whilst Leishmania-infected monocytes only made small contacts at a 5.5 µm(2) s(-1) ratio. The expression of high affinity epitope by VLA4 (from 39 ± 21% to 14 ± 3%); and LFA1 (from 37 ± 32% to 18 ± 16%) molecules was reduced in Leishmania-infected monocytes. These changes in phagocyte function may be important for parasite dissemination and distribution of lesions in leishmaniasis.

Fagócitos mononucleares inflamatórios potencialmente envolvidos no transporte de leishmania em hospedeiros vertebrados / Fagócitos mononuclear potentially inflammatory involved in the transport of leishmaniasis in vertebrate hosts

A infecção por protozoários do gênero Leishmania modula a função de integrinas em fagócitos inflamatórios. Essa alteração pode interferir na migração celular e apresentação de antígenos ao sistema imune. O objetivo deste estudo é identificar populações de fagócitos mononuc1eares inflamatórios potencialmente envolvidos no transporte de Leishmania em hospedeiros vertebrados. Inicialmente, definimos um modelo que permite o estudo do processo de migração em um grande número de fagócitos mononucleares inflamatórios. Para isso, foi induzida peritonite em camundongos da linhagem BALB / c com a injeção de Tioglicolato e foram examinadas a cinética de migração celular para o linfonodo regional e as populações de fagócitos mononuc1eares que compõem o exsudato e sua susceptibilidade à infecção com Leishmania. O influxo celular para o peritônio foi crescente, atingindo o pico de peritonite por volta do quarto dia. A partir de então, o número de células diminuiu, atingindo um platô por volta dos quarenta dias, permanecendo estável até o centésimo dia. Inicialmente, entre 4 horas e o primeiro dia, houve aumento de polimorfonuc1eares (9+ - 4 por cento, - 12+ - 8 por cento das células), seguindo um predomínio de fagócitos mononuc1eares (primeiro ao quarto dia) e posterior aparecimento de linfócitos (quadragésimo ao centésimo dia). A migração de fagócitos mononuc1eares para os linfonodos regionais foi observada 8 horas após o estímulo inflamatório, tornando-se máxima a partir do quarto dia. A migração das células foi confirmada em ensaios de injeção e rastreamento de células marcadas, observando-se a substancial migração dessas células para o linfonodo em um período de doze-vinte e quatro horas...