Myelin-phagocytosing macrophages modulate autoreactive T cell proliferation

Area of Science:

• Neuroimmunology
• Cellular immunology

Background:

• Multiple sclerosis (MS) is a CNS inflammatory disease involving macrophages.
• Macrophages' role in MS is complex, with myelin phagocytosis potentially altering their function.
• Myelin-laden macrophages in MS lesions suggest a potential immune regulatory role.

Purpose of the Study:

• To investigate the effect of myelin-phagocytosing macrophages on lymphocyte reactivity.
• To determine the mechanisms underlying macrophage-mediated immune modulation in the context of myelin.

Main Methods:

• Rat peritoneal macrophages were loaded with myelin and co-cultured with antigen-reactive lymphocytes.
• Lymphocyte proliferation was assessed using CFSE-labeling.
• In vivo studies involved myelin administration to immunized animals, followed by assessment of lymphocyte proliferation and nitric oxide (NO) production.

Main Results:

• Myelin-phagocytosing macrophages inhibit T-cell receptor (TCR)-triggered lymphocyte proliferation independently of antigen.
• This suppression is mediated by increased NO production by macrophages upon lymphocyte contact.
• In vivo, myelin delivery to macrophages in lymph nodes reduced antigen-specific proliferation in some contexts, but exacerbated it in others (e.g., myelin basic protein-reactive lymphocytes).

Conclusions:

• Myelin phagocytosis alters macrophage function, leading to inhibition of lymphocyte proliferation.
• Myelin-phagocytosing macrophages exhibit dual roles in vivo: suppressing general lymphocyte reactivity via NO and potentially aggravating autoimmunity by activating myelin-specific lymphocytes.