Here we study implications of Leishmania-host interaction by exploring Leishmania-infected dendritic cells migration. The differentiation and infection of dendritic cells, migration analysis, and the evaluation of adhesion complexes and actin dynamics are described. This method can be applied to other host cell migration studies when infected with Leishmania or other intracellular parasite species.
Leishmania is an intracellular protozoan parasite that causes a broad spectrum of clinical manifestations, ranging from self-resolving localized cutaneous lesions to a highly fatal visceral form of the disease. An estimated 12 million people worldwide are currently infected, and another 350 million face risk of infection. It is known that host cells infected by Leishmania parasites, such as macrophages or dendritic cells, can migrate to different host tissues, yet how migration contributes to parasite dissemination and homing remains poorly understood. Therefore, assessing these parasites’ ability to modulate host cell response, adhesion, and migration will shed light on mechanisms involved in disease dissemination and visceralization. Cellular migration is a complex process in which cells undergo polarization and protrusion, allowing them to migrate. This process, regulated by actin and tubulin-based microtubule dynamics, involves different factors, including the modulation of cellular adhesion to the substrate. Cellular adhesion and migration processes have been investigated using several models. Here, we describe a method to characterize the migratory aspects of host cells during Leishmania infection. This detailed protocol presents the differentiation and infection of dendritic cells, the analysis of host cell motility and migration, and the formation of adhesion complexes and actin dynamics. This in vitro protocol aims to further elucidate mechanisms involved in Leishmania dissemination within vertebrate host tissues and can also be modified and applied to other cell migration studies.
Leishmaniasis, a neglected tropical disease caused by protozoan parasites belonging to the genus Leishmania, results in a wide-ranging spectrum of clinical manifestations, from self-healing localized cutaneous lesions to fatal visceral forms of the disease. It has been estimated that up to one million new leishmaniasis cases arise annually, with a reported 12 million people currently infected worldwide1. Visceral leishmaniasis (VL), which can be fatal in over 95% of cases when left untreated, causes more than 50,000 deaths annually, affecting millions in South America, East Africa, South Asia, and the Mediterranean region2. The main etiological agent of VL in the new world, Leishmania infantum, is transmitted to humans by infected female sandflies during blood-feeding3. These parasites are recognized and internalized by phagocytes, e.g., macrophages and dendritic cells3,4,5. Inside these cells, parasites differentiate into their intracellular forms, known as amastigotes, which will then multiply and be transported via the lymphatic system and bloodstream to different host tissues6,7. However, the mechanisms by which Leishmania parasites are disseminated in the vertebrate host, as well as the role played by host cell migration in this process, remain unclear.
Cell migration is a complex process executed by all nucleated cells, including leukocytes8. According to the classic cycling model of cell migration, this process involves several integrated molecular events that can be divided into five steps: leading-edge protrusion; adhesion of the leading edge to matrix contacts; contraction of cellular cytoplasm; release of the rear edge of the cell from contact sites; and the recycling of membrane receptors from the rear to the front of the cell9.
For cell migration to occur, protrusions must be formed and then stabilized through attachment to the extracellular matrix. Among the different receptor types involved in the promotion of cell migration, integrins are notable. Integrin activation results in migration-related signaling; intracellular signaling then occurs via focal adhesion kinase (FAK) and Src family kinases, in addition to talin, vinculin, and paxillin molecues10,11,12. The phosphorylation of paxillin by activated kinases, including FAK, leads to the recruitment of effector molecules, which transduces external signals that prompt cell migration. It has been shown that paxillin is an intracellular molecule that is crucial to cell adhesion, actin polymerization, and cell migration processes13,14,15.
The actin cytoskeleton plays a central role in the polarization and migration of phagocytes16. During cell migration process, protrusions formed due to actin polymerization become stabilized through cell adhesion to the extracellular matrix. This process may be modulated by integrin receptors associated with the actin cytoskeleton17,18,19. Several actin-binding proteins regulate the rate and organization of actin polymerization in cellular protrusions20. Studies have shown that RhoA, Rac, and Cdc42 regulate actin reorganization after the stimulation of adherent cells by extracellular factors21,22. During migration, Rac1 and Cdc42 are located at the leading edge of the cell, controlling the extension of lamellipodia and filopodia, respectively, while RhoA, located at the rear of the cell, regulates the contraction of the actomyosin cytoskeleton15,23,24,25.
Studies have shown that Leishmania infection modulates host cell functions, such as adhesion to the cellular substrate and migration26,27,28,29,30,31. Immature DCs reside in peripheral tissues; upon interaction with PAMPS, these cells become activated and migrate to the draining lymph nodes, prompting antigen presentation to T cells. A previous study using a mouse model showed that L. amazonensis infection provokes a reduction in the migration of DCs to draining lymph nodes29. It was also demonstrated that the inhibition of the adhesion process reduced DC migration after infection with L. major30. Nonetheless, the impact of DC migration on parasite dissemination in the host, as well as the mechanisms involved in this process, remain poorly understood.
Here we present a compiled step-by-step protocol to perform an in vitro adhesion and migration assay involving human DCs infected by Leishmania. This method comprises not only the differentiation and infection of DCs, but also permits the analysis of host cell motility and migration, the formation of adhesion complexes, as well as actin dynamics. The presently described in vitro protocol allows researchers to further investigate the mechanisms involved in Leishmania dissemination within vertebrate host tissues and can also be manipulated and applied to other cell migration studies.
The method described here for evaluating cell migration using the cell culture membrane inserts system allows researchers to study the migratory response of cells in a two-dimensional environment. In this technique, some steps are considered critical. Firstly, the differentiation of human DCs and infection with Leishmania are determinative since the infection rate is donor-dependent. Using more than one donor per experiment and healthy Leishmania cultures will allow for more consistent results. It is al…
The authors have nothing to disclose.
This work was supported by Bahia Research Support Foundation (Fapesb), grant number 9092/2015. The authors acknowledge CNPq, Capes and Fapesb for financial support via scholarships. The authors would like to thank Andris K. Walter for critical analysis, English language revision and manuscript copyediting assistance.
16 Gauge needle | Descarpack | 353101 | |
24 well cell culture plate | JET-BIOFIL | J011024 | |
25 Gauge needle | Descarpack | 353601 | |
Albumin from bovine serum | Sigma Aldrich | A2153-100G | |
Ammonium chloride | Sigma Aldrich | A-0171 | |
Anti-mouse IgG, Alexa Fluor 488 | Invitrogen | A32723 | |
Anti-mouse IgG, Alexa Fluor 594 | Invitrogen | A11032 | |
Anti-rabbit IgG, Alexa Fluor 568 | Invitrogen | A11011 | |
CD14 MicroBeads | MACS Myltenyi Biotec | 130-050-201 | |
Cell Culture Flask 25cm2 | SPL | 70125 | |
Cellstripper | Corning | 25-056-CI | |
Confocal microscope | Leica | TCS SP8 | |
Coverslip circles 13mm | Perfecta | 10210013CE | |
Dissecting Forceps | VWR | 82027-406 | |
EDTA | Sigma Aldrich | E6758 | |
Falcon tube | KASVI | K19-0051 | |
Fetal Bovine Serum | gibco | 16000044 | |
Fluorescence microscope | Olympus | BX51 | |
Glass slide 25,4×76,2mm | Perfecta | 200 | |
Hemin bovine | Sigma Aldrich | H2250 | |
Hemocytometer | Perfecta | 7302HD | |
Histopaque® 1077 | Sigma Aldrich | 10771 | |
MACS buffer | MACS Myltenyi Biotec | 130-091-221 | |
Minimum Essential Medium | Gibco | 41090093 | |
Mouse anti-Rac1 | BD | 610650 | |
Paraformaldehyde | Sigma Aldrich | 158127 | |
Phalloidin Alexa Fluor 488 | Invitrogen | A12379 | |
Phosphate Buffered Saline | ThermoFisher | AM9624 | |
Polycarbonate Membrane Transwell Inserts – Pore size 5.0 µm | Corning | 3421 | |
ProLong Gold DAPI kit | Invitrogen | P36931 | |
Rabbit anti-Cdc42 | Invitrogen | PA1-092X | |
Rabbit anti-FAK (pTyr397) | Invitrogen | RC222574 | |
Rabbit anti-paxilin (pTyr118) | Invitrogen | QF221230 | |
Rabbit anti-RhoA | Invitrogen | OSR00266W | |
Recombinant Human CCL3 | R&D Systems | 270-LD-010 | |
Recombinant Human GM-CSF | PeproTech | 300-03 | |
Recombinant Human IL-4 | PeproTech | 200-04 | |
Recombinant Human M-CSF | PeproTech | 300-25 | |
RPMI 1640 Medium | Gibco | 21870076 | |
Saponin | Sigma Aldrich | 47036 – 50G – F | |
Syringe 3 mL | Descarpack | 324201 | |
Trypan Blue | Gibco | 15250061 |
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