Abstract: The present invention relates generally to the regulation of immune responses of subjects for the diagnosis and treatment of infertility. More particularly, methods that downregulate T helper 1 (Th1) immunity or upregulate T helper 2 (Th2) immunity are used to enhance reproductive outcomes in subjects with recurrent spontaneous abortions or implantation failures by changing the balance of T helper 1 and T helper 2 immune responses. Ratios of Th1 and Th2 activities can also be used for diagnosis of infertility in these subjects.