In addition and based on the recently published data of Motamedi et al. [60], we propose that the significantly elevated number of Gal-9+ NK cells in the PF of patients with endometriosis may mark functionally impaired killer cells, that express negligible amounts of perforin and granzyme (which is detrimental to their cytotoxic abilities) but can produce a high level of IFNγ, where the role is particularly highlighted in the pathogenesis of endometriosis. The gene discussed is PRF1; the disease is endometriosis.