Fasciola hepatica and Host Responses – A Network of

Intrigue

Grace Mulcahy UCD School of Veterinary Medicine

Oh what a tangled web we weave, When first we practise to deceive!

Sir Walter Scott, Marmion, Canto vi. Stanza 17.

Knowledge of Host Immune Responses

Vaccine Technology

Immunoregulation

Immune Responses of Cattle

•  Aged cows can be readily re-infected

•  Lymphocyte responsiveness correlates positively with fluke burden

(Clery et al., 1996)

•  After initial stimulation, lymphocyte and γ-INF responses are suppressed

(Clery and Mulcahy., 1996)

Cows

Heifers

Immune Responses of Cattle •  IgG1 is the dominant antibody class

•  Th0 and then Th2 clones are detected following infection (Brown et al. 1994)

•  Restimulation of PBMC induces IL-4 and IL-10

•  Multiple antigens recognised – ES antigens (Cathepsin L1) dominant

Log

Tit

re

Weeks post Infection

IgG1

IgG2

Vaccination using Cathepsin L1 Alters Antibody Isotype and Avidity

IgG1 IgG2

V V

C C

Macrophage Activation

Protection in low-challenge field trial

15

5.38 4.85

0

2

4

6

8

10

12

14

16

Control Adj A Adj B

Flukes

Fluk

e Num

bers

Summary

•  Immune responses of cattle infection permit chronic infection and do not prevent re-infection

•  Responses are associated with suppression of lymphocyte responsiveness, IgG1 dominance, altered macrophage phenotype and regulatory cytokine production

•  Vaccination with recombinant FhCL1 can induce balanced IgG1 and IgG2 responses, alter macrophage function, and induce partial protection.

What are the mechanisms of Fh-mediated Immunoregulation?

Macrophage Phenotypes and Pathways

Fh can induce AAMφ

•  Alternative Macrophage activation (Donnelly et al., 2005 – FhPrx)

•  AAMφ Ruminant-derived Macrophage cell line (Flynn et al., 2007)

Macrophage Activation

•  Regulatory cytokines IL-10 and TGF-β suppressing IFN-γ production

Regulatory cytokine induction

•  F. hepatica infection induces immune responses that permit persistence and re-infection

•  Alternative-activation of macrophages and the regulatory cytokines TGF-β and IL-10 are implicated in Fh-mediated immunoregulation

•  Some vaccine protocols can disrupt this process and deliver partial immunity

Is Fh-mediated immunoregulation important to anyone other than vaccinologists?

Recap

Potential Global Implications 0f Macroparasite-mediated Immunoregulation

Hygiene Hypothesis and inflammatory disease

Bystander Immunoregulation and Chronic infection

Helminth inflammatory/Immune effects in Animal Health

•  Salmonella? •  Clostridial Diseases? •  Mycobacterial

infection •  Disease diagnosis •  Response to Vaccines

Is the Immunoregulatory Effect of Practical Significance?

F. hepatica/M. bovis co-infection

Wk 0 Wk 4 Wk 13 Wk 14

F.h M.b SCITT PME

Group-1 F. Hepatica

150 metacercariae Aerosol M. bovis

5x102 cfu n = 6

Aerosol M. bovis 5x102 cfu

n = 6

Group-2

Fh Mb

Reduction of INF-γ Production

Co-infection increases IL-10 Response to M. bovis

Intradermal Response to PPD Challenge

0

5

10

15

20

25

30

Mb Fh/Mb

Series1

PPDB-

PPDA

M Bovis M Bovis/Fh

Role of Granulomatous Inflammation?

•  In vitro bovine granuloma model

•  Effect of Fh products

Macrophage phenotype

Granuloma morphology

Bacterial fate

Fh products

Thanks to…..

Rob Flynn Olwen Golden Elaine McCarthy Olwen Golden Lindsey Cox

Jim McNair Michael Welsh Sam Strain

Diana Williams