Protection against anti-citrullinated protein antibody-positive rheumatoid arthritis is predominantly associated with HLA-DRB1*1301: a meta-analysis of HLA-DRB1 associations with anti-citrullinated protein antibody-positive and anti-citrullinated protein antibody-negative rheumatoid arthritis in four European populations. - van der Woude D; Lie BA; Lundström E; Balsa A; Feitsma AL; Houwing-Duistermaat JJ; Verduijn W; Nordang GB; Alfredsson L; Klareskog L; Pascual-Salcedo D; Gonzalez-Gay MA; et al. (Arthritis & Rheumatism, 2010)