An Exploration of the Dynamic Interaction Between IL-17, IL-17 Inhibition With (Secukinumab) and Neutrophils in Psoriatic Arthritis in Vitro and ex Vivo With Exploratory Study on the Potential Role of Vitamin D

The investigators propose an open label pragmatic clinical and laboratory study designed to investigate, in detail, the clinical and molecular effects of Interleukin 17 (IL-17) and inhibition of IL-17 with secukinumab, on neutrophil function in vitro and ex vivo.

As secondary, exploratory objectives, the investigators will utilise the fact that secukinumab is to be administering to 20 patients with Psoriatic Arthritis (PsA) and investigate whether there is any relationship between vitamin D status and response to secukinumab, with respect to efficacy and adverse events. The results of this secondary exploratory analysis will inform the design of a larger, definitive study.