Phylogenetic Development of Lymphoid Compartments

With the development of adaptive immunity, the requirement of specialized organs for antigen (Ag) presentation, clonal expansion of T and B lympho cytes, and affinity maturation of B lymphocytes has evolved. Such secondary (immune response-generating) lymphoid organs have B and T cell compartments and are found in all jawed vertebrates. The capacity to form germinal centers (GCs) after immunization and hence, efficient production of high-affinity antibodies (Abs) is a major advantage of...

Conclusions and Perspectives

Complex metazoans coexist with different types of microorganisms ranging from overt pathogens to beneficial symbionts. This co-existence requires that the host (a) be able to mount protective immune responses to potential pathogens, (b) allow for the mutualist microbes to confer benefit to host biology, (c) prevent constitutive immune responses to the indigenous microbes that would cause immune-mediated pathology, and (d) prevent opportunistic infections caused by endogenous pathogens...

Regulation of Atopic Allergic Responses

The hygiene hypothesis suggests that the absence of microbial infection may lead to the development of IgE-mediated atopic allergy by Th2-polarized immune responses (Strachan 1989 Umetsu et al. 2002). It is hypothesized that this may occur through the lack of microbial induced Th1 responses and associated with increased Th2 responses, or by a defective generation of immunoregulatory mediators such as regulatory T cells or interleukin-10 (Macpherson and Harris 2004). Evidence that the indigenous...