A revised view of the central nervous system microenvironment and major histocompatibility complex class II antigen...

Area of Science:

• Neuroimmunology
• Cellular immunology
• Central Nervous System (CNS) research

Background:

• Phagocytes expressing Major Histocompatibility Complex (MHC) Class II molecules are observed in the CNS under normal and pathological conditions.
• MHC Class II expression is crucial for antigen presentation to CD4+ T-cells, but requires co-stimulatory molecules for full activation.

Purpose of the Study:

• To review in vivo studies on the immune response capabilities of microglia and perivascular macrophages within the CNS.
• To elucidate the role of CNS-resident myeloid cells in initiating and supporting immune responses.

Main Methods:

• Review of recent in vivo studies examining immune cell function in the CNS.
• Analysis of in vitro studies investigating microglial interactions with T-cells.

Main Results:

• Microglia and perivascular macrophages in the CNS are incapable of initiating primary immune responses.
• These cells can, however, support secondary immune responses within the CNS.
• In vitro, microglia can induce apoptosis in autoreactive T-cells, potentially protecting the CNS.

Conclusions:

• The CNS microenvironment limits the initiation of primary immune responses by resident myeloid cells.
• This limitation may compromise immune surveillance, allowing pathogens to persist undetected in the CNS.
• Microglia play a role in modulating T-cell responses, including inducing apoptosis of autoreactive T-cells.