This document summarizes the proposed mechanisms behind ankylosing spondylitis (AS), a type of arthritis that mainly affects the lower spine. It discusses how the presence of the HLA-B27 protein, found in over 95% of Caucasians with AS, may lead to inflammation through aberrant antigen processing and presentation. Specifically, mutations in HLA-B27 or the protein ERAP1, which helps cleave antigens for presentation, could cause immune responses through endoplasmic reticulum stress or inability to associate antigens with HLA-B27. Additional factors like the IL-23 pathway may also contribute to AS development. Genome-wide studies have identified other genetic loci associated with AS risk.

1. Inflammatory Effects of HLA-B27 as a Mechanism in
Ankylosing Spondylitis
Jordan Meyers

2. • Ankylosing Spondylitis
Overview
• Proposed Mechanism
• Roles of ERAP1 and HLA-B27
• Other Possible Causes
• Discovery of new AS-associated
loci
• Conclusion, Acknowledgements

3. What is Ankylosing Spondylitis?
• Arthritis that affects mainly the lower
vertebrae.
• Exact mechanism of the disease is
unknown
• Symptoms:
• Inflammation
• Soreness in lower back
• Stiffness in lower back
• Gastrointestinal irregularities
• Other areas that can be affected:
• Eyes
• Hips
• Ribs
• Lungs (rarely)

4. What we do know:
• Of the Caucasian population with a
confirmed diagnosis, >95% test positive
for Human Leukocyte Antigen – B27
(HLA-B27).
• This protein consists of 90 Amino Acids:
• GSHSMRYFHT SVSRPGRGEP RFITVGYVDD
TLFVRFDSDA ASPREEPRAP WIEQEGPEYW
DRETQICKAK AQTDREDLRT LLRYYNQSEA
• Most likely mechanism through which AS
operates is through an aberrant
processing of antigenic peptides.

5. Proposed Mechanism – What causes inflammation?
• HLA-B27 is one type of a major
histocompatibility complex that
presents antigens to CD8 lymphocytes
(T-cells) on the cell’s surface.
• Any type of mutation in the protein
can cause an aggregation of ‘unfit’
proteins in the Endoplasmic
Reticulum, which causes stress.
• The immune system responds by
generating pro-inflammatory cytokines
and chemokines.

6. Role of ERAP1
• ERAP1 serves as a ‘molecular ruler’ – it
cleaves proteins that have been partially
processed by the proteosome into
smaller peptides for association with
MHC class I proteins.
• MHC = Major Histocompatibility
Complex, AKA Human Leukocyte
Antigens (HLA’s).
• Single Nucleotide Polymorphs of ERAP1
can alter its efficiency, resulting in the
inability of peptides to associate with
HLA-B to be presented to the cell
surface.
• Shown Right: mean rate of cleavage of
N-Terminal Tryptophan residue in 10-
mer peptide, WRVYEKCALK, by ERAP1
Wild Type, and AS associated mutants. Evans, Spencer et al, 2011

7. Other possible causes of AS
• The IL-23 – IL-23R – IL-17 is also suspect
in the mechanism of AS.
• Studies have shown that an
overexpression of Tumor Necrosis Factor
Receptor 1 (TNFR1) is sufficient to
induce spondyloarthritis in mice.
• Further research is required to
determine if SNPs at the locus involved
in production of TNFR1 (12p13) are
associated with AS.
Iwakura and Ishigame, 2006

8. Discovery of new AS-associated loci
• SNPs at the RUNX3 loci may induce AS
through lowered CD8+ lymphocyte
counts
• RUNX3 is a key gene that encodes a
transcription factor involved in CD8+
lymphocyte differentiation
• CARD9, PTGER4
• CARD9 – mediates signals from
dectin-1 and -2, which are immunity
receptors for β-glucan. Mice treated
with higher amounts of β-glucan
developed spondyloarthritis.
• PGE2 acts through PTGER4 to
promote expansion of TH17 cell
counts (Evans et al, 2011).

9. Conclusion
• Most likely mechanism through with AS
develops is through an aberrant processing
of antigenic peptides, or their presentation
to CD8+ lymphocytes on the cell surface.
• HLA-B27 plays a predominant role in the
pathogenesis of the disease, but AS can still
develop even in cases in which HLA-B27 is
not present.
• Genes strongly associated with
pathogenesis of AS: IL23R, RUNX3, KIF21B,
2p15, IL12B, ERAP1, HLA-B, LBTR-TNFR1,
and 21q22 (Evans et al, 2011).
• Further 4 loci identified: ANTXR2, PTGER4,
CARD9, TBKBP1 (Evans et al, 2011).

10. Literature Cited
Evans, David M.; Spencer, Chris C A.; Pointon, Jennifer J.; Su, Zhan;
Harvey, David; Kochan, Grazyna; Oppermann, Udo; Dilthey, Alexander;
Pirinen, Matti; Stone, Millicent A; Appleton, Louise;
Moutsianas, Loukas; Leslie, Stephen; Wordsworth, Tom; Kenna, Tony J;
Karaderi, Tugce; Thomas, Gethin P; Ward, Michael M;
Weisman, Michael H; Farrar, Claire; Bradbury, Linda A; Danoy, Patrick;
Inman, Robert D; Maksymowych, Walter; Gladman, Dafna;
Rahman, Proton; Morgan, Ann; Marzo-Ortega, Helena; Bowness, Paul;
Gaffney, Karl; Gaston, J S Hill; Smith, Malcolm; Bruge-Armas, Jacome;
Couto, Ana-Rita; Sorrentino, Rosa; Paladini, Fabiana; Ferreira, Manuel
A; Xu, Huji; Liu, Yu; Jiang, Lei; Lopez-Larrea, Carlos; Diaz-Pena, Roberto;
Lopez-Vazquez, Antonio; Zayats, Tetyana; Band, Gavin;
Bellenguez, Celine; Blackburn, Hannah; Blackwell, Jenefer M.;
Bramon, Elvira; Bumpstead, Suzannah J.; Casas, Juan P.; Corvin, Aiden;
Craddock, Nicholas; Deloukas, Panos; Dronov, Serge;
Duncanson, Audrey; Edkins, Sarah; Freeman, Colin; Gillman, Matthew;
Gray, Emma; Gwilliam, Rhian; Hammond, Naomi; Hunt, Sarah E.;
Jankowski, Janusz; Jayakumar, Alagurevathi; Langford, Cordelia;
Liddle, Jennifer; Markus, Hugh S; Mathew, Christopher G.;
McCann, Owen T.; McCarthy, Mark I.; Palmer, Colin N A.;
Peltonen, Leena; Plomin, Robert; Potter, Simon C.; Rautanen, Anna;
Ravindrarajah, Radhi; Ricketts, Michelle; Samani, Nilesh;
Sawcer, Stephen J.; Strange, Amy; Trembath, Richard C.;
Viswanathan, Ananth C.; Waller, Matthew; Weston, Paul;
Whittaker, Pamela; Widaa, Sara; Wood, Nicholas W.; McVean, Gilean;
Reveille, John D.; Wordsworth, B Paul; Brown, Matthew A.;
Donnelly, Peter. 2011. “Interaction between ERAP1 and HLA-
B27 in ankylosing spondylitis implicates peptide handling
in the mechanism for HLA-B27 in disease susceptibility.”
Nature Genetics. Vol. 43:8. Pp 761-767.

11. Acknowledgments
• UMD Chemistry and
Biochemistry Department