Leprosy Immunopathogenesis The famous Sun temple Konark By Jean-Marie Doze What is common in all these slides ? Leprosy does not differentiate between man and God Even Gods are Afraid of Leprosy Why do I say this ? Shri Ram contracted Kushtha, cured after taking the fruit of the chaulmoogra tree. Alfica Sehgal. First edition. Leprosy. Philadelphia: Chelsea Publishers; 2006 Samba cured after worshipping the Sun god at Konark. www.templenet.com ―Jesus heals a leper and cautions silence, but the man didn‘t keep quiet, so Jesus could no more openly enter into the city.‖ Mark 1:40-45 What is leprosy ? It is a chronic granulomatous disease of the skin and peripheral nerves with intracellular bacterium M. leprae. Clinically characterized by Hypopigmented patches Loss of cutaneous sensation Thickened nerves AFB in skin/nasal smears History Earliest references in Hindu texts 600 BC Chinese literature ‗Nei Ching ` 500 BC Dark ages lepers buried alive or burnt. Mass of separation History contd.. Danielson Father of leprology Gives first scientific account Establishes that leprosy is a inherited disease History contd.. Gerhard Henrick Armauer Hansen Danielson`s son in law Discovered M. leprae To get rid of the stigma disease is named as Hansens disease in 1892 History contd .. Dr. J.F.Mouat, of the Bengal Medical Service in 1853 used Chaulmogra seeds and published his findings in the Indian Medical Journal 1943- Introduction of promin , a sulfone drug for leprosy treatment 1950s- Dr. R.G. Cochrane was a pioneer in the use of dapsone 1960- Shepard- limited multiplication in mouse foot pad 1962- Ridley & Jopling-classification based on immunity History contd.. 1970s- Success at last! Drug trials on the island of Malta in the 1970s led to an effective combination of drugs to treat leprosy. 1981- WHO started MDT 1997- Elimination by 2000, then 2005 2001- genome sequenced 2005- eliminated in most parts of world Current Status 2008: 118 countries and territories, the global regstd prevalence at beginning of 2008 is 212,802 cases, the number of new cases during 2007 was 254,525 No. of new cases detected globally fallen by 11,100 cases (a 4% decrease) during 2007 compared with 2006 Has achieved the goal of elimination of leprosy as a public health problem, defined as less than 1 case per 10,000 population, at the National Level in the month of December, 2005. 6 states viz Bihar, Chhattisgarh, Jharkhand, Orissa, UP & West Bengal; & 3 Uts namely Chandigarh, Dadar & Nagar Haveli, & Delhi have prevalence rate between 1-2/ 10,000 population. Contribute to 67% of recorded case load & 66% of new cases detected during 2005-06. Park`s Textbook of P&SM Leprosy: A neglected disease When compared to Tuberculosis Why are people scared of Leprosy? Agent: Mycobacterium leprae Nonmotile Non-sporeforming 1-8 microns length, 0.2-0.5 u diameter Acid fast (5% sulphuric acid) Usually forms slightly curved or straight rods Appear as agglomerates-bacilli bound by lipid like substance-‖globi‖ Parallel rows of bacilli in globi-cigar bundle appearance Intracellular Longest doubling time 12-13 days(8-42 days) Not culturable in vitro Affinity for skin, nerves-low temp. Protein antigens 65 kDa ◦ 95% homology with M tb, M bovis, BCG ◦ Seropositivity implies high bacillary load 70 kDa, 28kDa, 7 kDa, 14 kDa Unknown fn- 36,18,30/31 kDa Genome "Massive gene decay in the leprosy bacillus" Nature 409, 1007-1011 (2001). This ―minimal gene set‖, the result of extensive gene deletion and decay that have eliminated many key metabolic pathways, renders the leprosy mycobacterium extremely slow in replicating and forces it to an intracellular existence. This loss of genes- dependence on highly specialised ecological niches for survival Reservoir Humans ◦ multibacillary cases-LL- BL (4-11X than TT) ◦ TT??(all pts with active leprosy) ◦ In apparent infections Natural infn with M. leprae ◦ Armadillos ◦ Mangabey monkey ◦ Cynomolgous macacque Armadillo ◦ Only occ. cases in humans handling armadillos ◦ Max. cases in India-no armadillos Infectivity Incubation period –few mths-30 yrs Highly infectious disease of low pathogenicity Attack rate ◦ 4.4-12% of household contacts show signs of leprosy within 5 years ◦ 5% of spouses living with leprosy patients Modes of Transmission Droplet infection ◦ Aerosols containing M. leprae (LL- 8×108 bacilli in one nose blow) Contact transmission (prolonged, close) ◦ Direct- even thro intact skin ◦ Indirect (fomites, soil) Long survival in soil-studies Modes of Transmission: Doubtful Other routes ◦ Congenital? (M. leprae in sperm, ovary, umbl cord, placenta, fetus) ◦ Insect vectors (mechanical transfer) ◦ Tattooing needles, penetrating wounds How does a person develop leprosy? Two-step model for development of leprosy Step 1 Infection develops in Genetically predisposed . Step 2 Subsequent clinical manifestations host & environmental factors. Casanova JL, Abel L. Genetic dissection of immunity to mycobacteria: the human Genetic factors: Innate Overall susceptibility/resistance to infection • Mediated by cells of monocyte lineage • Candidate genes or loci –PARK2/PACRG- leprosy per se –NRAMP1(natural resistance asso. M Ø protein)- LL Genetic factors contd.. • Degree of specific cellular immunity & DTH generated by infected individual • Mediated through T lymphocytes and APC • Candidate genes/loci –HLA , chromosome 10p13, TNF receptor, TAP, Toll like receptor, vitamin D receptor Genetic factors: Acquired Immunity • HLA – DR2, DR3 associated with TL, – DQ1 asso .with LL • Chromosome 10p13 – Genomewide linkage scan of 244 families in S. India- significant linkage of microsatellite markers on this chromosome with susceptibility – Most pts had TL Genetic factors contd.. • Chromosome 6q25 Lancet ;April 2003 • TAP – TAP 2 gene associated with TL • TNF alpha – Associated with resistance to M. leprae – High levels in pts with TL • Toll like receptors – TLR important for pathogen recognition – TLR2 controls prodn of cytokines, cell signaling, other aspects of resist. to M. leprae • VDR – Different alleles of human vitamin D receptor gene –asso. with different forms Environment • Presence of infectious cases in envt. – Humidity favors survival • Viable in dried nasal secretions-9 days • Moist soil at RT- 46 days – Overcrowding, lack of ventilation • Larger households (> 7 members) 3X risk as compared to 1-4 member household – Social factors governing contact TLR,DC Sign , C lectin receptors(DC) Recognizes Pathogen associated molecular pattern Produce Transcription factors Induce Effector molecules(Cytokines) Activation of APC Antigen processing(Lipid ) Presented on CD1 molecule CD 1 restricted T cells are activated Th1 response Th2 response Spectrum Innate immune response Underhill and Ozinsky. Annu. Rev. Immunol. 2002 Mechanism of Mycobacterial killing • IFN γ mediated macrophage activation • Generation of ROI • Production of NO and RNI • Cytotoxic/NK cell mediated killing Evasion ◦ Inhibit lysosomal fusion ◦ Resist digestion ◦ Oxygen scavenging-PGL1, LAM ◦ Enzyme induction-catalase, SOD ◦ Stress response- hsp Pathogenesis of Leprosy • Factors determining position in spectrum – Environmental factors – Infectious dose – Differential suppression of CMI – Genetic factors • All immune responses-need APC-express Ag information on surface& along with MHC initiate immune cascade • Normal macrophages imp.- Mitsuda positive and negative clones evolve into different APC-asso with CMI or humoral immunity respectively Polarity of disease TT ◦ vigorous immune response ◦ disease ltd to well defined skin patches, nerve trunks ◦ Lesions infiltrated by IFN gamma secreting CD4+ Tcells ◦ well formed granulomas ◦ few AFB Polarity of disease LL ◦ absence of specific cellular immunity ◦ uncontrolled proliferation of bacilli ◦ many lesions,extensive infiltration of skin, nerves ◦ Dermis has foamy macrophages filled with bacteria ◦ Few CD4+, CD8+ t lyphocytes, no organised granulomas ◦ High titres of antibodies to PGL1 & protein antigens of M leprae • Macrophages- central role –bipolar in action • In Mitsuda positive pts – Macrophages destroy all bacilli-obtain normal antigenic formation to act as APC-stimulate CMI-form epitheloid granulomas-few bacilli • In Mitsuda negative – Only partial lysis of bacilli-bacterial phospholipids persist – Lepra cells/virchowcytes appear (macrophages that have partially digested the bacilli PL) – Antigenic information incomplete-cells cannot act as APC Immune mechanisms in lepromatous leprosy • Incomplete expression of Ag-macrophages fail to act as APC-formation of lepra cells • Lepra cells may undergo apoptosis or may be phagocytosed by other Mitsuda negative macrophages • These obtain complete neoantigen informationact as new APCs-when asso with MCH IIsecretes IL4-incites humoral immunity linked CD4+ cells Immune mechanisms in lepromatous leprosy • Acivation of B cells-anti M leprae serum antibodies, IL-1, TNF alpha produced • Cytokines leads to Type 2 leprosy reactions-Erythema nodosum leprosum • If circulating complexes existleucocytoclastic vasculitis type 3 reactions (Lucio phenomena) Cellular responses in leprosy skin lesions ◦ T cells expressing γδ T cells & αβ T cells ◦ These recognise non peptide antigens (LAM,mycolic acid)-presented by CD1 molecules on APC independent of HLA class I or II ◦ CD1 expressed on dendritic cells of TT pts not LL ◦ CD1 restricted T cells contribute to control of pathogen Reactions in leprosy • Reactional states in leprosy are episodes of immunologically mediated acute or subacute inflammation in skin, nerves, eyes and other sites superimposed on underlying chronic states. Type I Reaction • Seen in borderline Leprosy because of their immunological instability • Gradual onset, increased induration & erythema of existing lesions • Associated with a shift in immunity • May or may not be associated with treatment Pathogenesis • Coombs & Gell Type IV DTH • Ags from breaking down Lepra bacilli react with T cells & this is assoc with rapid change in CMI • Assoc with a shift in patients‘ position in the spectrum Cytokine profile • Increased—IL-1 ,TNF-, IL-2, IFN- • Decreased IL-4,IL-5,IL-10 • Hence it‘s a Th1 response with suppression of Th2. Type 2 reactions • Occurs almost exclusively in LL, occasionally in BL. • Sudden onset • Many erythematous tender nodules on face, extremities, trunk- no relation to previous lesion Type 2 reactions • Type III Hypersensitivity Reaction • Genetic basis for ENL—Patients with a genetic polymorphism in the promotor region of the TNF gene(TNF 2) are at higher risk of developing LL Type 2 reactions • Mainly Th2 response: This T cell population provides help to B cell antibody production resulting in M. leprae specific humoral response. • IL-8 is a potent chemotactic factor for Pathogenesis Humoral and CMI operate principal event –deposition of antigenantibody complex in tissues. In LL-most are CD8+ cells, but when ENL starts ▼ Macrophages present M. leprae antigens ▼ Infiltration of CD4+ cells to dermis ▼ Growth factors for mast cells, IL-4, IL-5, IL-10 ▼ Stimulate antibody release Immune complex deposition takes place ▼ Complement stimulation ▼ Neutrophils chemotaxis,TNF- levels increased ▼ Fever and tissue damage What is the mechanism of nerve injury ? Bacteremia perineural tissue Taken up by Schwann cells(PGL1laminin complex ) no phagolysozyme formation intracellular niche Direct W/O early cell death Immune Prodn of infl cytokines TNF-α IL-1β, & interferon-γ Others 19 Kda Ag induces apoptosis or Apoptosis How have we gained this knowledge ? Nine banded armadillo (Dasypus novemcinctus) ◦ ◦ ◦ ◦ Leprosy like disease -1975 Agent identical to humans-1985 Highly endemic normal host of M leprae Exotic looking cat sized animal with short legs ◦ Pig in turtle shell with malformed head ◦ 3-5 kg, 12-15 yrs life span ◦ USA, Mexico, some countries in S. America Animal models Rodents Thymectomised & irradiated mice Nude congenitally athymic mice SCID mice iNOS knock out mice Animal models contd.. Non human primates ◦ Chimpanzees ◦ Monkeys Sooty mangabey monkey Cynomolgus monkey African green monkey Animal models contd.. Susceptible to infection with M leprae ◦ Golden hamsters ◦ Indian Pangolin ◦ Korean chipmunks Any vaccines against leprosy ?? So Leprosy is chronic mycobacterial disease Presents as a spectrum Science is like looking through a keyhole: The closer you get to the keyhole, the more you see of the room on the other side. -George Wald 1967 Nobel Laureate in Medicine Thank you Immunopathogenesis of leprosy Dr.Vinaykumar . Hallur