B-cells need a proper house, whereas T-cells are happy in a cave: the dependence of lymphocytes on secondary lymphoid tissues during evolution.
A fundamental tenet of immunology is that adaptive immune responses are initiated in secondary lymphoid tissues. This dogma has been challenged by several recent reports. We discuss how successful T cell-mediated immunity can be initiated outside of such dedicated structures, whereas they are required for adaptive humoral immunity. This resembles an ancient immune pathway in the oldest cold-blooded vertebrates, which lack lymph nodes and sophisticated B-cell responses including optimal affinity maturation. The T-cell, however, has retained the capacity to recognize antigen in a lymph node-free environment. Besides bone marrow and lung, the liver is one organ that can potentially serve as a surrogate lymphoid organ and could represent a remnant from the time before lymph nodes developed.
Hofmann
Janin
J
Division of Neuroimmunology, Inst. Exp. Immunology, Department of Pathology, University Hospital of Zurich, 8057 Zurich, Switzerland.
Greter
Melanie
M
Du Pasquier
Louis
L
Becher
Burkhard
B
D056704:Adaptive Immunity; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D005075:Biological Evolution; D007113:Immunity, Innate; D008221:Lymphoid Tissue / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*