PATHOBIOLOGY AND IMMUNOLOGY

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PATHOBIOLOGY AND IMMUNOLOGY OF ACANTHAMOEBA
KERATITIS
Jerry Y. Niederkorn University of Texas
Southwestern Medical Center Dallas, Texas
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QUESTIONS

• DO CORNEAL INFECTIONS WITH ACANTHAMOEBA
• INDUCE ADAPTIVE IMMUNITY?
• WHICH IMMUNE ELEMENTS CONFER PROTECTION
• AGAINST AK?
• HOW DOES ACANTHAMOEBA PRODUCE DISEASE?
• 4. ARE THERE ADDITIONAL RISK FACTORS THAT
• AFFECTAK?

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PIG AND CHINESE HAMSTER MODELS OF ACANTHAMOEBA
KERATITIS
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DO CORNEAL INFECTIONS WITH ACANTHAMOEBA ELICIT
ADAPTIVE (T CELL-DEPENDENT) IMMUNE RESP0NSES?
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CORNEAL ACANTHAMOEBA INFECTIONS FAIL TO INDUCE
T CELL-MEDIATED AND T CELL-DEPENDENT IMMUNE
RESPONSES
1. DTH RESPONSES ARE UNDECTABLE DURING OR
AFTER OCULAR INFECTIONS (CHINESE
HAMSTERS) 2. IN VITRO T CELL LYMPHOPROLIFERATIVE
RESPONSES ARE NOT DETECTED IN INFECTED
PIGS, BUT ARE FOUND IN PIGS IMMUNIZED I.M.
WITH ACANTHAMOEBA ANTIGENS (PIGS). 3.
ACANTHAMOEBA KERATITIS DOES NOT ELICT SERUM IgG
ANTIBODY PRODUCTION (PIGS AND CHINESE
HAMSTERS)
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DOES ENVIRONMENTAL EXPOSURE TO ACANTHAMOEBA SPP.
ELICIT IMMUNE RESPONSES?
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NATURALLY OCCURRING SERUM ANTIBODIES IN
INVIDUALS WITH NO HISTORY OF AK

• 50 OF INDIVIDUALS TESTED WERE SEROPOSITIVE
  (Cerva, L.,
• Jour Hyg Epidem Microbiol Immunol 1989)
• 100 (N88) OF NORMAL ADULTS AND CHILDREN WERE
• SEROPOSITIVE (Cursons et al. Infect Immun
  1980)
• 100 (N25) OF NORMAL INDIVIDUALS WERE
  SEROPOSITIVE
• (Alizadeh et al. Cornea 2001)
• 100 (N23) OF AK PATIENTS WERE SEROPOSITIVE
• (Alizadeh et al. Cornea 2001)

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EXTRAOCULAR IMMUNIZATION WITH ACANTHAMOEBA
TROPHOZOITES DOES INDUCE T CELL-DEPENDENT IMMUNITY

• STRONG DTH RESPONSES
• T CELL LYMPHOPROLIFERATIVE RESPONSES
• IgG COMPLEMENT-FIXING ANTIBODIES
• SECRETORY IgA ANTIBODIES (MUCOSAL)

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ALTHOUGH CONVENTIONAL T CELL- AND
ANTIBODY-DEPENDENT IMMUNE RESPONSES CAN BE
ELCITED, THEY FAIL TO PREVENT OR MITIGATE
ACANTHAMOEBA KERATITIS.

• I.M. IMMUNIZATION WITH EITHER ACANTHAMOEBA
• ANTIGENS OR TROPHOZOITES ELICITS
  ACANTHAMOEBA-
• SPECIFIC SERUM IgG AND DTH, YET FAILS TO
  PROTECT EITHER
• PIGS OR CHINESE HAMSTERS AGAINST AK (Clarke
  and
• Niederkorn, Microbes and Infection 2006)
• 2. 100 OF THE NORMAL POPULATION, INCLUDING AK
  PATIENTS
• POSSESS SERUM IgG ANTIBODIES SPECIFIC FOR
• ACANTHAMOEBA ANTIGENS (Alizadeh, et al.
  Cornea 2001).
• 3. TROPHOZOITES ARE RESISTANT TO
  COMPLEMENT-DEPENDENT
• CYTOLYSIS (Alizadeh et al., Cornea 1995
  Toney et al. Jour
• Parasitol 1998)

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IF THE ADAPTIVE IMMUNE SYSTEM CANNOT KILL
ACANTHAMOEBA TROPHOZOITES, CAN IT BE ENGAGED TO
PREVENT TROPHOZOITES FROM GAINING A FOOTHOLD AT
THE OCULAR SURFACE?
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SECETORY IgA ANTIBODIES

• MORE IgA IS PRODUCED DAILY THAN ALL
• OTHER ANTIBODY ISOTYPES COMBINED.
• SECRETORY IgA IS A POOR COMPLEMENT
• FIXING ANTIBODY AND DOES NOT FACILITATE
• ADCC.
• SECRETORY IgA IS EXCELLENT NEUTRALIZING
• AND BLOCKING ANTIBODY.

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SECRETORY IgA ANTI-ACANTHAMOEBA ANTIBODIES
PROTECT AGAINST AK

• ORAL IMMUNIZATION ELICITS ANTI-ACANTHAMOEBA IgA
• ANTIBODIES IN TEARS (PIGS AND HAMSTERS)
• ANTI-ACANTHAMOEBA IgA ANTIBODIES PREVENT
• TROPHOZOITE BINDING TO CORNEAL EPITHELIAL
  CELLS (PIGS
• AND HAMSTERS)
• ORAL IMMUNIZATION PREVENTS AK IF GIVEN PRIOR TO
• OCULAR CHALLENGE , BUT FAILS TO AFFECT
  ONGOING
• INFECTIONS (PIGS AND HAMSTERS)
• PASSIVELY TRANSFERRED ANTI-ACANTHAMOEBA
  MONOCLONAL
• IgA ANTIBODY PREVENTS AK (HAMSTERS)
• AK PATIENTS HAVE SIGNIFICANTLY LOWER
  ANTI-ACANTHAMOEBA IgA ANTIBODIES IN THEIR TEARS

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ANTI-ACANTHAMOEBA IgA ANTIBODIES BLOCK THE FIRST
STEP IN THE PATHOGENIC CASCADE OF ACANTHAMOEBA
KERATITIS
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MANNOSE-BINDING PROTEIN (MBP) IS A CRUCIAL LIGAND
FOR ADHESION TO THE CORNEAL EPITHELIUM
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IS THE MANNOSE-BINDING PROTEIN AN EFFECTIVIE
IMMUNOGEN FOR PROTECTING AGAINST AK?
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ORAL IMMUNIZATION WITH ACANTHAMOEBA
MANNOSE-BINDING PROTEIN AMELIORATES ACANTHAMOEBA
KERATITIS
Garate et al. Infect Immun 2006
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MUCOSAL IMMUNIZATION WILL PREVENT INFECTION, BUT
CAN WE TARGET PATHOGENIC MOLECULES AND PRODUCE AN
ANTI-DISEASE VACCINE?
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MANNOSE-INDUCED PROTEASE -133 (MIP-133)

• INDUCED WHEN TROPHOZOITES BIND TO THE CORNEA
• INDUCES APOPTOSIS OF CORNEAL CELLS
• FACILITATES INVASION AND DISSOLUTION OF STROMA
• MANNOSYLATED PROTEIN DEPOSITS ON CONTACT
  LENSES
• INDUCE MIP-133 PRODUCTION
• CONTACT LENS WEAR UPREGULATES MANNOSYLATION OF
  
• CORNEAL PROTEINS
• TRAUMA TO CORNEA UPREGULATES MANNOSYLATION
• BACTERIAL FLORA (CORYNEBACTERIUM) CAN INDUCE
  MIP-133
• UPREGULATION OF MIP-133 EXACERBATES ACANTHAMOEBA
• KERATITIS

Leher et al. Infect Immun. 1998 Alizadeh et al.
Infect Immun 2005 Hurt et al. IOVS 2003 Hurt et
al. Infect Immun 2003
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CAN WE USE MIP-133 AS AN ANTI-DISEASE VACCINE?
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ORAL IMMUNIZATION WITH MIP-133 MITIGATES
ACANTHAMOEBA KERATITIS IN HAMSTERS
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SUMMARY

• IMMUNE EFFECTOR CELLS AND ANTIBODIES ARE
• INEFFECTUAL IN KILLING ACANTHAMOEBA
• TROPHOZOITES AND CYSTS.
• MUCOSAL ANTIBODIES (TEARS) DIRECTED AGAINST THE
• BINDING LIGAND (MBP) FOR ACANTHAMOEBA
• TROPHOZOITES PREVENT THE INITIAL INFECTION,
  BUT
• HAVE NO EFFECT ONCE TROPHOZOITES HAVE GAINED
  A
• FOOTHOLD IN THE CORNEA.
• MUCOSAL IMMUNIZATION WITH MIP-133 IS AN
• EFFECTIVE ANTI-DISEASE STRATEGY.

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• MANNOSYLATED PROTEINS ON THE CORNEAL EPITHELIUM
  ARE IMPORTANT LIGANDS FOR TROPHOZOITE ADHESION.
  BINDING STIMULATES MIP-133 RELEASE.
• 5. MANNOSE IN BACTERIAL FLORA (C. XEROSIS) OF THE
  CONJUNCTIVA CAN INDUCE MIP-133 RELEASE AND
  EXACERBATE AK.
• CONTACT LENS WEAR UPREGULATES MANNOSYLATED
• PROTEIN EXPRESSION IN THE CORNEA. THIS INDUCES
  MIP-133 RELEASE AND INCREASES CORNEAL CELL
• DAMAGE AND STROMAL MELTING.

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CONCLUSIONS PATHOLOGY

• MANNOSYLATED PROTEINS FACILITATE TROPHOZOITES
• BINDING TO THE CORNEA AND TRIGGER
  ACANTHAMOEBA
• TROPHOZOITES TO RELEASE PATHOGENIC PROTEASES
  (e.g.
• MIP-133).
• MANNOSYLATED PROTEINS ON CONTACT LENSES AND ON
• BACTERIAL FLORA IN THE CONJUNCTIVA EXACERBATE
  THE
• PATHOGENESIS OF ACANTHAMOEBA KERATITIS.
• CONTACT LENS WEAR UPREGULATES MANNOSYLATED
• PROTEINS ON THE CORNEAL SURFACE AND
  FACILITATES
• BINDING AND RELEASE OF MIP-133.

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CONCLUSIONS IMMUNOLOGY

• ADAPTIVE IMMUNE ELEMENT ARE INEFFECTUAL IN
  KILLING
• TROPHOZOITES AND CYSTS.
• BLOCKING THE INITIAL ADHESION OF TROPHOZOITES
  TO THE
• CORNEAL SURFACE IS THE ONLY EFFECT IMMUNE
  MECHANISM
• THAT CAN PREVENT OR CONTROL CORNEAL INFECTION
  WITH
• ACANTHAMOEBA.
• TROPHOZOITES PRODUCE SERINE PROTEASES THAT
  KILL
• CORNEAL CELLS, FACILITATE INVASION, AND
  DISSOLVE THE
• STROMA.
• THESE SERINE PROTEASES ARE TARGETS FOR
  ANTI-DISEASE
• VACCINES.

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THOSE WHO DESERVE THE CREDIT
UT SOUTHWESTERN
LEIDEN UNIVERSITY
Hassan Alizadeh H. Dwight Cavanagh Daniel
Clarke YuGuang He Kevin Howard Michael Hurt Henry
Leher James McCulley Sudha Neelam
Martine Jager Floor van Klink
TUFTS UNIVERSITY
Marco Garate Noorjanhan Panjwani
UNIVERSITY OF SYDNEY
Kathy McClellan
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DOES THE IMMUNE PRIVILEGE OF THE EYE PREVENT
THE INDUCTION OF T CELL-DEPENDENT IMMUNE
RESPONSES TO ACANTHAMOEBA INFECTIONS?