Earlier the presence of peripheral lymphoid organs hosting immune reactions against infections was considered by lymphocyte-centered researchers as a set of tissues throughout the body being conveniently present when leukocytes need them almost akin to deus ex machine, for either as specific homing destinations after the lymphocytes have differentiated in primary lymphohemopoietic organs or sites of immune responses. A major emphasis had been placed on the availability of lymphocytes of appropriate clonal composition and maturation status, without much consideration for the three-dimensional mesenchymal architecture of the lymphoid organs the majority of these hemopoietic cells reside in, until some key discoveries concerning the development of secondary lymphoid tissues were made. Thus following several decades of a rather quiet flow of classical embryological studies with relatively little attention in general biomedical research, however, the investigations addressing the formation of peripheral lymphoid organs have now gained a strong momentum, transforming this area into one of the most rapidly developing fields connecting developmental biology to basic and clinical immunology. Advances along three main avenues have been crucial to the renewed interest. First, our improved ability to identify minor (hemopoietic as well as stromal) cell populations by a continuously growing range of suitable markers, cell separation instruments, and procedures has greatly facilitated the characterization, high-speed purification, and subsequent analysis of cell subsets of major significance in this developmental process. Second, the expansion of procedures in genetic manipulation for targeted mutagenesis and regulated gene expression/deletion and the resulting plethora of transgenic mice have also been instrumental for revealing the role of several target cells and their progeny as well as key molecules in the process. Finally, the advances in bioinformatics with high throughput analyses have provided insight into the intracellular molecular mechanisms and developmental responses following interaction of several receptor and ligand pairs not only in physiological developmental events, but also in various pathological conditions mostly associated with chronic inflammations and lymphoid malignancies. Thus, the impact of identifying key elements goes beyond understanding the physiological lymphoid organ development and its role for improved efficiency in normal immune responses; it may also provide opportunities to ameliorate pathological conditions related to aberrant lymphoid tissue formation.
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)