Leishmania Flashcards
Interactions of Leishmania with host immune system
Important for parasite survival and immunopathologies.
Leishmania and the immune system; parasite survival.
Apoptosis (parasite and target cells).
Overcoming leishmanicidal activity.
Altering signalling.
Modulating cellular function.
Leishmania and the immune system; immunopathologies.
CL and VL pathogenesis.
Treatment and vaccines.
Leishmania and the immune system; parasite survival, APOPTOSIS
Apoptotic parasites
Inhibiting apoptosis in target cells: neutrophils, macrophages and dendritic cells, and T cells.
Leishmania and the immune system; parasite survival, OVERCOMING LEISHMANICIDAL ACTIVITY.
Glycocalyx
Defence against AMPs.
Phagosome maturation.
Leishmania and the immune system; parasite survival, ALTERING SIGNALLING.
To increase T cell apoptosis. Altering TLR signalling. Influencing chemokine induction. Affecting intracytosolic signallng. Infect stromal cells.
Leishmania and the immune system; parasite survival, MODULATING CELLULAR FUNCTION.
Decreasing presentation
DC cells
Induction of anergy
T cell exhaustion.
Leishmania and the immune system; parasite survival, apoptosis, APOPTOTIC PARASITES.
Dead parasites appear to be essential for successful infection by live parasites. Exposure of phosphotidylserine leads to silent invasion, stimulating production of anti-inflammatory cytokines like TGF-B.
Leishmania and the immune system; parasite survival, apoptosis, APOPTOSIS IN TARGET CELLS.
Neutrophils
Macrophages
Dendritic cells
T cells.
Leishmania and the immune system; parasite survival, apoptosis, APOPTOSIS IN NEUTROPHILS.
Controversial
Delay
Induction
Trojan horse
Leishmania and the immune system; parasite survival, apoptosis in neutrophils, delay
Protection of safe intracellular niche via activation of ERK1/2. Allows time for arrival of APCs – act as depots, allowing adaptation for survival in macrophages.
Recruitment of APCs important for longer term infection.
Leishmania and the immune system; parasite survival, apoptosis in neutrophils, induction.
Induce apoptosis in some studies. Possibly passage through neutrophils allows released parasites to be better adapted for macrophage survival? In L. major, studies suggest aid life cycle progression.
Leishmania and the immune system; parasite survival, apoptosis in neutrophils, trojan horse.
Uptake and degradation of neutrophils by macrophages –> uptake of parasites –> TGF-B production. (Trojan horse model) But yet to be confirmed in vivo.
Leishmania and the immune system; parasite survival, apoptosis, APOPTOSIS IN MACROPHAGES AND DENDRITIC CELLS.
Purpose of delay of apoptosis.
Mechanism
Leishmania and the immune system; parasite survival, apoptosis in macrophages and dendritic cells, purpose.
Delay apoptosis –> time to differentiate into amastigotes, good host cells for replication. But dendritic cells not ideal as important in antigen presentation and stimulation of Th1 protective response.
Leishmania and the immune system; parasite survival, apoptosis in macrophages and dendritic cells, mechanisms.
Via induction of TNFa signaling
Preventing ATP induced cytolysis
Production of homologue of macrophage inhibiting factor induces ERK1/2.
L. major appear to act via Akt pathway.
Induction of cell-to-cell transfer of amastigotes in membrane blebs. Prevents full exposure to external milieu, and allows quiescent invasion.
Leishmania and the immune system; parasite survival, apoptosis of T cells
Mechanisms unknown, but may involve downregulation and dephosphorylation of molecules in TCR pathway.
Leishmania and the immune system; overcoming leishmanicidal activity, GLYCOCALYX
Important in complement and phagocytosis.
Involves LPG, GP63 and GIPL.
Leishmania and the immune system; overcoming leishmanicidal activity, glycocalyx, complement.
Avoid MAC: LPG prevents attachment of C5b-C9 complex, GP63 inactivates C3b –> iC3b.
Enhance complement cascade (and hence opsonisation). iC3b still acts as an opsonin.
Leishmania and the immune system; overcoming leishmanicidal activity, glycocalyx, phagocytosis.
Enhance phagocytosis – opsonisation, plus GP63 and LPG bind receptors. LPG also interacts with CRP, which increases phagocytosis.
Leishmania and the immune system; parasite survival, overcoming leishmanicidal activity. PHAGOSOME MATURATION.
Delay lysosomal fusion.
Inhibit oxidative stress.
Leishmania and the immune system; parasite survival, overcoming leishmanicidal activity, phagosome maturation, DELAY LYSOSOMAL FUSION.
promastigotes cannot survive the phagolysosome, so this delay is necessary to allow differentiation. LPG insertion into lipid microdomains important.
LPG prevents fusion with tertiary and specific granules responsible for acidification and superoxide production. Also decreases recruitment of v-ATPase.
Involvement of ER communication with phagosome.
Some spp: large parasitophorous vacuoles lead to dilution below level needed to kill promastigotes.
Leishmania and the immune system; parasite survival, overcoming leishmanicidal activity, DEFENCE AGAINST AMPS.
GP63 important: gp63 KO killed in dose dep manner by AMPs.
Leishmania and the immune system; parasite survival, overcoming leishmanicidal activity, phagosome maturation, INHIBIT OXIDATIVE STRESS.
TGF-B shifts arginine metabolism to production of ornithine. –> decrease in NO secretion
Suppression of iNOS expression by GILP
Intrinsic antioxidant machinery
Leishmania and the immune system; parasite survival, altering signalling, TLR SIGNALLING. .
MAPK inactivation –> downregulates IL-12 production –> less pro-inflammatory response.
Activate TLR2?
TLR alteration highly complex, needs more research. L. donovani exploits host negative regulator.
Leishmania and the immune system; parasite survival, altering signalling, INFLUENCING CHEMOKINE INDUCTION.
1) IL-4 and IL-10 - induce, immunosuppressive.
2) IL-12 affects production of IFN-y, IL-10 and IL-4. Some species decrease IL-12 production by decreasing cholesterol, and so affect these others.
3) Upregulate chemokines chemotactic for neutrophils and Th2 cells.
4) Possible interactions with Tregs leads to downregulation of IFN-y, upregulation of IL-10.
Leishmania and the immune system; parasite survival, altering signalling, HOW DO THEY AFFECT INTRACYTOSOLIC SIGNALLING?
Target phosphotyrosine phosphatases.
Target PKC and NFkB.
Leishmania and the immune system; parasite survival, altering signalling, intracytosolic signalling, PHOSPHOTYROSINE PHOSPHATASES.
Some proteins cross using cholesterol –rich lipid rafts. E.g. GP63 does this and cleaves SHP1, an important phosphotyrosine phosphatase. SHP1 important in anti-leishmanial immunity, as when active inhibits JAK3 and Erk1/2 pathways.. Different L. spp have different GP63s; exact role unclear. GP63 has promiscuous action: can cleave several proteins. Also interferes with TLR pathways.
Leishmania and the immune system; parasite survival, altering signalling, intracytosolic signalling, TARGETTING PKC AND NFkB.
Some species seem to express molecules with PKC like activity.
NFkB often hyporesponsive. Some species have been reported as promoting differential expression patterns by promoting NFkB p50-p50 dimers, rather than p65-p50 dimers.
Disrupt antigen presentation by decreasing cholesterol synthesis.
Leishmania and the immune system; parasite survival, altering signalling, INFECTION OF STROMAL CELLS.
Attract DC cells that reduce effectiveness of Th1 response.
Leishmania and the immune system; parasite survival, modulating cellular function. DECREASED PRESENTATION.
Downregulation class II MHC and co-stim molecules.
o Sequester antigens from presentation pathway.
o Inefficient engagement of MHC II-peptide complexes and TCRs by altering membrane fluidity and lipid rafts.
Leishmania and the immune system; parasite survival, modulating cellular function. DCs.
Inhibiting DC activation, inducing maturation arrest
Immunopathology CL
Th1/Th2 Infiltration of neutrophils Keratinocyte signalling Lymphadenopathy vs healing. T cells.
Immunopathology CL - Th1/Th2.
Th1 promotes parasite killing, Th2 promotes disease dissemination.
Immunopathology CL, neutrophils.
Involved in protection and pathology.
Rapid infiltration, trojan horse model.
Recruitment of monocytes.
Immunopathology CL, neutrophils. RAPID INFILTRATION.
Possible role of alarmins, release of cytokines by sentinel cells, and co-injection of bacteria with parasites by sandfly.
Immunopathology CL, KERATINOCYTES.
IL-6 production important in innate resistance.
Intrinsic antioxidant machinery.
Trypanothione synthase and reductase.
Immunopathology CL, LYMPHADENOPATHY.
Cells migrate to lymph nodes -> lymphadenopathy –> activation of adaptive response –> IFN-y production by T cells –> activation of leukocytes –> immune mediated inflammation –> high concentration of inflammatory mediators –> necrosis and apoptosis. Tissue destruction apparently necessary for parasite clearance.
Immunopathology CL, HEALING.
Chronic cells, collagen production and etc –> healing.
Immunopathology CL, T CELLS.
Mechanisms to study
MCL/DCL, cutaneous lesions.
Th1 response
Role of CD8 cells unclear.
Immunopathology CL, mechanisms to study.
Whole blood stimulation, Leishmanin skin test.
Immunopathology CL, MCL/DCL, cutaneous lesions.
Responses tend to be hyper responsive in MCL, hyporesponsive in DCL
Cutaneous lesions: abundant, activated CD4 and CD8 T cells. A large proportion bear TCRγδ, which is unusual.
Immunopathology CL, Th1 response
Th1 response promotes killing, but regulatory responses induced by the parasite can lead to susceptibility by making macrophages unresponsive, so persistence of parasite chronic inflammation and tissue destruction. Key source of IL-10.
Immunopathology, VL
General
Balance of responses
Arms of response
Things affecting progression.
Immunopathology, VL, general.
Fatal systemic infection, with parasitisation of spleen, liver and bone marrow.
Depressed cell mediated responses.
Immunopathology, VL, balance of responses.
No Th2 skewing. Previously thought that TH1 responses were defective, but recent study stimulation of whole blood with crude Leishmania antigen has increased TH1 responses.
o VL induction is determined by the balance of pro versus anti inflammatory cell mediated responses.
Generally 4 weeks post infection shows granuloma formation in the liver
Chronic infection in the spleen. Immune suppression in this organ due to micro effects and structural alterations in macroarchitecture due to loss of marginal zone macrophages, partly due to TNF-a production.
Immunopathology, VL, arms of the response
Dysfunctional presentation Neutrophils T cells IL-10 B cells.
Immunopathology, VL, arms of the response, dysfunctional presentation.
See MHC interactions.
Also, receptors appear important: dectin-1 and mannose receptors favour antiparasitic response, whereas DC-SIGN homologue in mice inhibited IL-1B production and lead to parasite persistence. IL-1B critical for inducing reactive nitrogen intermediates in macrophages.
• IL-10 also targets antigen presentation.
Immunopathology, VL, arms of the response, neutrophils.
Important early in control – but in CL models act as safe haven. Do they in VL?
Immunopathology, VL, arms of the response, T cells.
Th1 CD8 Dysfunctional T cells Th17 Tregs Memory
Immunopathology, VL, arms of the response, Th1.
TH1 –> IFNy –> activates macrophages for parasite killing. Active VL leads to a robust IFNy response, and a signature high IL-10 response. Many other people are asymptomatic when infected with L. donovani or L. infantum, probably due to several factors including
Immunopathology, VL, arms of the response, CD8.
usually exhausted phenotype in VL (High production of CTLA-4 and PD-1), but if present can contribute to both pathology and protection. Cytotoxic activity, IFNy production, regulatory capacity. Important at start of infection if infected with low dose.
Immunopathology, VL, arms of the response, dysfunctional T cells.
CD4 T cells critical in resolution as important in granuloma formation, important in cellular recruitment and in activating infected macrophages to achieve killing. T cell dysfunction due to Tr1 IL-10 production, suppressing production of IFNy by CD4 T cells, and downregulating antigen presentation.
Immunopathology, VL, arms of the response, Th17.
o Proinflammatory, induce expression of innate inflammatory mediators.
o Produce IL-17: associated with resistance.
o In VL, IL-27 may block Th17 expansion, and promote IL-10 cells.
Immunopathology, VL, arms of the response, T reg.
o Natural vs adaptive?
o Highly associated with disease and pathology. Affect macrophages. Foxp3 important.
Different in different infections: protective in L. panamensis, but cause pathogenesis for VL species.
Immunopathology, VL, arms of the response, memory T cells.
o Effector memory vs central memory?
o Parasite persistence even after clinical cure.
o Multi-functional CD4 cells most protective. Produce IFNy, IL-2 and TNF-a.
Immunopathology, VL, arms of the response, IL-10.
- Key immunoregulator. From many immune cells.
- Blockade promotes parasite killing, overexpression leads to unrestrained parasite replication.
- Leads to inappropriate immune damage too. Also true for other pathogens e.g. plasmodium and trypanosomes. In murine model, IL10 -/- KO mice were reported to be resistant, but without increased tissue pathology or mortality due to excessive inflammation.
- Neutralisation beneficial in human infection?
Immunopathology, VL, arms of the response, B cells.
- Ab importance unclear
* High Ab titres in active cases. May lead to immune complexes stimulating IL-10 production?
What affects VL progression?
Type of parasite
Genetic basis
Environmental factors
What affects VL progression, type of parasite.
Genetic differences
Tissue tropism
What affects VL progression, type of parasite. Genetic differences.
Some studies –> chromosome and gene copy number variations between species could be responsible for the varying ability of species of the L. donovani complex to cause visceral disease.
What affects VL progression, type of parasite. Tissue tropism
It has also been suggested that the tropism could be due to temperature sensitivity requirements to survive in visceral organs. I am not aware whether the latter is supported by further scientific evidence.
What affects VL progression, host genetics.
Mouse studies.
Human studies.
What affects VL progression, host genetics. Mouse studies.
- Slc11a1. Different alleles resistance/susceptibility? Slc11a1 involved in proton/divalent cation transport and promote phagosome/lysosome cellular fusion. Also decreases iron availability in phagosome.
- In susceptible, MHC class II alleles determine resolution later in disease. If successful, leads to formation of granulomas.
What affects VL progression, host genetics. Human studies.
• Why?
o Mouse studies (see above) suggest maybe.
o Familial clustering
o Ethnic differences in VL susceptibility
o High relative risk in further siblings of affected sibling pairs.
• Slc11a1 associations. No functional coding region in humans –> no effect.
• Genome wide association studies other candidates
o HLA-DR-DQ
o Some Indian studies chemokine receptors are important.
What affects VL progression, environmental factors.
Malnutrition
Co-infections.
What affects VL progression, environmental factors. Malnutrition.
Altered cytokine production.
Negatively impacts both cell-mediated and innate immunity.
What affects VL progression, environmental factors. Co-infections.
HIV. Same population at risk. 70% of VL cases associated with HIV.
o Abrogation of host T cell response skews away from Th1, poor leishmanicidal activity.
o Pro-inflammatory response hasten progression to AIDS.
Helminths
o Poor hygiene and malnutrition.
o Helminths promote TH2.
o No formal demonstration of relationship.
Immunopathology, treatments and vaccines.
o Asymptomatic infections occur where there is a strong cell-mediated response.
o Drugs are toxic, so poor compliance and increasing resistance.
o Lifelong resistance from cure of asymptomatic infections.
o No available vaccine, but given rapid and lasting immune response, seems possible.
o Vaccination strategies
Immunopathology, treatments and vaccines. Vaccine strategies.
Live vaccination – only used in Uzbekistan. Leishmanisation. Not tested against VL, only cutaneous forms. May lead to complications, so largely not done.
Whole killed Leishmania
Recombinant proteins, polyproteins and DNA vaccines
Altering immune response with adjuvants
Live attenuated or live non-pathogenic
Could we get immunity from more than one species with a single vaccine.
Phases of self-resolving cutaneous leishmaniasis.
Acute (local inflammation, uptake by neutrophils).
Silent (monocyte wave)
Active phase (adaptive response, keratinocytes, nercrosis)
Ulcerative phase (mostly adaptive)
Healing phase/Chronic phase/Non-ulcerative DCL.
Effect of IL-12
Pushes to Th1 phenotype producing IFNy, macrophage M1 activation and elimination of parasites.
Downregulation of IL-12
Decreased TLR signalling,
Inhibit assembly of CD40 signalosome, or deactivate downstream.
Th1 cytokines result in
macrophage M2 phenotype and susceptibility.
Class and order,
Class = kinetoplastids, Order = trypanosomatids
Transmission
Transmitted by sandflies – zoonotic in New World, anthroponotic in Old World. Many vector species. Many parasite species, at least 2 natural animal reservoirs.
Form in sandfly.
Promastigote – extracellular, flagellated, 15 um (transform to promastigote in sandfly midgut)
Form in mammal.
Obligate intracellular. Generally infect macrophages, but can infect other haemopoietic cells (neutrophils etc) or some non-haemopoietic cells (e.g. fibroblasts.
Non-flagellated
3-4 um
Amastigote
Epidemiology
o Dates to at least 1st century AD.
o Geography: tropical and subtropical regions (vector selectivity?). Urbanisation spread.
Changes in distribution - factors.
Climate change Environmental changes Socioeconomic factors Population mobility Malnutrition Males overreport – tropism?
