Spleen in innate and adaptive immunity regulation

The spleen is a large secondary lymphoid organ located in the blood-stream, primarily functioning as a massive blood filter. It filtered effete red blood cells, antigen-antibody complexes, apoptotic bodies, damaged cells, among others. Spleen's myriad microanatomy reflects the diversity and complexity of its functions. As a specialized immune organ, the spleen immune system plays a significant role in innate and adaptive immunity. Specialized innate immune cells like B cells, natural killer (NK) cells, and macrophages populate locations within the spleen. Specifically, the spleen is a crucial organ for peripheral immune tolerance, complementing central immune tolerance. Spleen remains the only organ in the body capable of mounting an appropriate immune response to encapsulated bacteria. Spleen houses tolerogenic immune cells like [CD8.sup.+] Treg cells, F4/80+ macrophages, [CD68.sup.+]F4/[80.sup.+] red pulp macrophages, [CD169.sup.+] metallophillic macrophages, [CD8.sup.+]CD205+ splenic dendritic cells (DCs), splenic CD8[[alpha].sup.+][CD103.sup.+][CD207.sup.+] DCs, [CD43.sup.+ve][CD19.sup.hi][CD5.sup.+ve]Ig[M.sup.hi]Ig[D.sup.lo] B cells, and splenic NKT cells that express regulated on activation normal T cell expressed and secreted (RANTES/CCL5) chemokine. Splenocytes are extra-thymic autoimmune regulator gene (AIRE) expressing cells that regulate tissue-specific antigens' expression to confer peripheral immune tolerance. As such, the spleen provides the right site for counteracting autoimmunity. Splenectomy in both study animals and humans results in overwhelming infections with, especially encapsulated bacteria. The anterior chamber-associated immune deviation (ACAID) is closely related to the spleen that needs to be studied to improve transplant survival. The role of the spleen in anti-tumor immunity yields an inconclusive result. In-depth research is needed to find which cells or pathways are linked to favorable outcomes concerning cancer. Understanding the spleen's microanatomy and physiology will provide a framework for treating diseases, especially autoimmune diseases, cancer, infections, and transplantation. Keywords: spleen; innate immunity; adaptive immunity; immune privilege; peripheral tolerance; anterior chamber-associated immune deviation (ACAID)