Research letter

The role of T helper 25 cells in the immune response to Mycobacterium leprae

Leprosy, a disease caused by Mycobacterium leprae, has polymorphic neurocutaneous manifestations strongly correlated with the host immune response. Peripheral neural damage can lead to sensory and motor losses, as well as deformities of the hands and feet. Both innate and acquired immune responses are involved, but the disease has been classically described along a Th1/Th2 spectrum, where the Th1 pole corresponds to the more limited presentations and the Th2 to the multibacillary ones. The aim of this review is to discuss this dichotomy in light of the current knowledge of the cytokines, T helper subpopulations, and regulatory T cells involved in each presentation of leprosy. The text will also address leprosy reactions related to increased inflammatory activity in both limited and multibacillary presentations, leading to exacerbation of chronic signs and symptoms and/or the development of new ones. Despite the efforts of many research groups around the world, there is no standardized serological test/biological marker for diagnosis so far, even in endemic areas, which could contribute to the eradication of leprosy.

The immune system is made up of cells and molecules that protect the host body from harmful stimuli and keep the body in a state of homeostasis. The immune system's components respond in a coordinated and comprehensive manner, resulting in the emergence of an “immune response.” There are two types of immunity: innate and adaptive immune systems. The initial line of defense against infections is the innate immune system, which responds rapidly to stimuli. The adaptive immune system identifies antigens more specifically than the innate immune system and can produce memory cells which have the ability to react quickly to pathogens in the second encounter. In this chapter, we sought to present the fundamental principles of the immune system, covering the key components of lymphoid organs, immune system structure, innate and adaptive immunity, as well as the basic effective functions of the immune system to pathogen eradication.