A method of diagnosing rheumatoid arthritis in a subject comprising evaluating a biological sample which has been obtained from the subject and determining whether the subject is immunologically reactive with one or more of filamin-A and N-acetylglucosamine-6-sulfatase, by: (i) detecting the presence of T cells by: a) stimulating peripheral blood mononuclear cells (PBMC) or synovial fluid mononuclear cells (SFMC) of the subject in vitro with one or more of filamin-A and N-acetylglucosamine-6-sulfatase, whole protein or polypeptide fragment; b) measuring T cell proliferation in vitro or secretion of IFN-γ into cell culture supernatants; and c) identifying the subject as having T cells reactive to one or more of filamin-A and N-acetylglucosamine-6-sulfatase when T cell proliferation or secretion of IFN-γ is increased over that of an appropriate control; and/or (ii) determining if the subject has a B-cell response to one or more of filamin-A and N-acetylglucosamine-6-sulfatase resulting in the production of autoantibodies that specifically recognize the one or more filamin-A and N-acetylglucosamine-6-sulfatase, by contacting the sample with filamin-A protein or a polypeptide fragment thereof, and/or N-acetylglucosamine-6-sulfatase protein or a polypeptide fragment thereof, under conditions that allow an immunocomplex of the antibody and the filamin-A or N-acetylglucosamine-6-sulfatase form, and detecting the presence or absence of an immunocomplex, wherein the presence of an immunocomplex indicates the subject presents a B-cell response to filamin-A and/or N-acetylglucosamine-6-sulfatase and wherein the absence of an immunocomplex indicates the subject fails to present a B-cell response to filamin-A and/or N-acetylglucosamine-6-sulfatase; wherein the polypeptide fragment of filamin-A comprises the amino acid sequence NPAEFVVNTSNAGAG (SEQ ID NO: 1) or an antigenic portion thereof, and wherein the polypeptide fragment of N-acetylglucosamine-6-sulfatase comprises the amino acid sequence of FEPFFMMIATPAPH (SEQ ID NO: 2) or an antigenic portion thereof. (i) detecting the presence of T cells by: a) stimulating peripheral blood mononuclear cells (PBMC) or synovial fluid mononuclear cells (SFMC) of the subject in vitro with one or more of filamin-A and N-acetylglucosamine-6-sulfatase, whole protein or polypeptide fragment; b) measuring T cell proliferation in vitro or secretion of IFN-γ into cell culture supernatants; and c) identifying the subject as having T cells reactive to one or more of filamin-A and N-acetylglucosamine-6-sulfatase when T cell proliferation or secretion of IFN-γ is increased over that of an appropriate control; and/or a) stimulating peripheral blood mononuclear cells (PBMC) or synovial fluid mononuclear cells (SFMC) of the subject in vitro with one or more of filamin-A and N-acetylglucosamine-6-sulfatase, whole protein or polypeptide fragment; b) measuring T cell proliferation in vitro or secretion of IFN-γ into cell culture supernatants; and c) identifying the subject as having T cells reactive to one or more of filamin-A and N-acetylglucosamine-6-sulfatase when T cell proliferation or secretion of IFN-γ is increased over that of an appropriate control; (ii) determining if the subject has a B-cell response to one or more of filamin-A and N-acetylglucosamine-6-sulfatase resulting in the production of autoantibodies that specifically recognize the one or more filamin-A and N-acetylglucosamine-6-sulfatase, by contacting the sample with filamin-A protein or a polypeptide fragment thereof, and/or N-acetylglucosamine-6-sulfatase protein or a polypeptide fragment thereof, under conditions that allow an immunocomplex of the antibody and the filamin-A or N-acetylglucosamine-6-sulfatase form, and detecting the presence or absence of an immunocomplex, wherein the presence of an immunocomplex indicates the subject presents a B-cell response to filamin-A and/or N-acetylglucosamine-6-sulfatase and wherein the absence of an immunocomplex indicates the subject fails to present a B-cell response to filamin-A and/or N-acetylglucosamine-6-sulfatase;