Thymulin (also known as thymic factor or its old name facteur thymique serique) is a nonapeptide produced by two distinct epithelial populations in the thymus first described by Bach in 1977.

The hormone is believed to be involved in T-cell differentiation and enhancement of T and NK cell actions.

There exist bidirectional interactions between thymic epithelium and the hypothalamus-pituitary axis (for example, thymulin follows a circadian rhythm and physiologically elevated ACTH levels correlate positively with thymulin plasma levels and vice versa[2]).

A recent focus has been on the role of thymulin as an effector on proinflammatory mediators/cytokines.

Researchers hope to develop drugs thwarting inflammatory processes associated with neurodegenerative diseases and even rheumatism with the help of thymulin analogs.