Introduction:
Prolactin (PRL) is a 23-kDa protein that can be synthesized and secreted by pituitary and extrapituitary tissues such as immune cells due to its expression being regulated by two independent promoter regions. The promoter which is responsible for extrapituitary expression contains the single nucleotide polymorphism (SNP) –1149 G/T previously associated with autoimmune diseases in various populations. This study evaluates the relationship of PRL –1149 G/T polymorphism with PRL serum levels and clinical characteristics in systemic lupus erythematosus (SLE) patients from western Mexico.

Material and methods:
One hundred and sixty-three SLE patients classified according to the 1982 American College of Rheumatology (ACR) SLE classification criteria and 326 unrelated control subjects (CS), both from western Mexico, were included. The PRL –1149 G/T polymorphism was genotyped using the polymerase chain reaction restriction fragment length polymorphism technique, and both PRL serum levels and autoantibodies were measured by enzyme-linked immunosorbent assay (ELISA).

Results:
We found an association between the PRL –1149 TT genotype and SLE according to the recessive genetic model (OR = 2.26, 95% CI: 1.01–5.08, p = 0.04). The TT genotype was associated with anti-RNP antibodies (p = 0.04) and with higher scores of the Mex-SLEDAI (p = 0.02). Moreover, SLE patients showed elevated PRL serum levels (12.4 ng/ml; p < 0.01), and this condition was associated with renal activity and the presence of anti-RNP antibodies.

Conclusions:
PRL –1149 TT genotype is associated with susceptibility to SLE in a Mexican-Mestizo population, and high PRL serum levels are associated with anti-RNP antibodies and renal activity.