Leucine-rich repeat kinase 2 (LRRK2) is the causal molecule of familial Parkinson's disease (PD). but its true physiological function remains unknown. In the normal mouse, LRRK2 is expressed in kidney, spleen, and lung at much higher levels than in brain, suggesting that LRRK2 may play an important role in these organs Analysis of age-related changes in LRRK2 expression demonstrated that expression in kidney, lung. and various brain regions was constant throughout adult life Oil the other hand, expression of both LRRK2 mRNA and protein decreased markedly in spleen in an age-dependent manner Analysis of purified spleen cells indicated that B lymphocytes were the major population expressing LRRK2, and that T lymphocytes showed no expression Consistently, the B lymphocyte surface marker CD19 exhibited an age-dependent decrease of mRNA expression in spleen These results suggest a possibly novel function of LRRK2 in the immune system, especially in B lymphocytes (C) 2010 Elsevier Inc All rights reserved