The present disclosure relates to antibodies and proteins comprising an antigen-binding portion thereof that specifically bind to the pro-inflammatory cytokine IL-17 A. The disclosure more specifically relates to specific antibodies and proteins that are IL-17 A antagonists (inhibit the activities of IL-17 A and IL-17 AF) and are capable of inhibiting IL-17 A induced cytokine production in in vitro assays, and having an inhibitory effect in an antigen-induced arthritis model in vivo. The disclosure further relates to compositions and methods of use for the antibodies and proteins to treat pathological disorders that can be treated by inhibiting IL-17A or IL 17AF mediated activity, such as rheumatoid arthritis, psoriasis, systemic lupus erythematosus (SLE), lupus nephritis, chronic obstructive pulmonary disease, asthma or cystic fibrosis or other autoimmune and inflammatory disorders.