Role of CD138⁺ Plasma Cells and Natural Killer Cells in Couple Infertility: A Review

Couple infertility is a multifactorial condition that involves, among other factors, immunological alterations of the endometrium. CD138⁺ plasma cells and uterine Natural Killer (NK) cells have been associated with implantation failures and recurrent pregnancy loss, although the literature presents considerable heterogeneity in findings. This narrative review aims to synthesize current evidence on the role of these two immunological biomarkers in the pathophysiology of infertility. According to the current literature, the presence of CD138⁺ plasma cells was strongly associated with chronic endometritis and adverse reproductive outcomes, with improvement following targeted antibiotic therapy. NK cells, particularly in their hyperactive peripheral form, were elevated in infertile women, although data on uterine NK cells remain controversial. Recent studies suggest a possible interaction between chronic inflammation and NK dysfunction. A combined evaluation of CD138⁺ and NK cells may represent an integrated diagnostic approach in idiopathic infertility. Prospective studies are needed to standardize cut-off values and validate these markers in clinical practice.