PDE4A and systemic lupus erythematosus: MRL/lpr lupus-prone mice have been treated with PDE inhibitors with different selectivity and specificity toward PDE4, namely pentoxifylline characterized by a lack of PDE isoform selectivity, denbufylline displaying a higher selectivity for PDE4, and NCS 613 characterized by a high selectivity for PDE4 and a strong potency (Tables 2 and 3).