Morphological view on the evolution of the immunity and lymphoid organs of vertebrates, focused on thymus

Abstract

To understand fundamental defense mechanisms of an individual and to perceive organization and functioning of the human immune system, it is inevitable to sum up its phylogenic development. Lymphoid organs are crucial in regulation of physiological lymphocytes development and subsequently play a significant role in appropriate immunological responses to foreign pathogens. Throughout the evolutionary tree, the primary lymphoid organs have emerged earlier than the secondary lymphoid organs. Considering the sites for cell populations’ development responsible for adaptive immunity, B lymphocytes differentiation and maturation have considerably differed during phylogeny as well as ontogeny. On the contrary, T lymphocytes development is defined exclusively in the thymus. From the evolutionary point of view, location of primary lymphoid organs must have been sophistically pre-programmed in terms of their function. Need for thymus evolving from the foregut supports the fact of emerging diverse repertoire of antigen receptors. The thymus represents the very first lymphoid organ evolved in Vertebrata to deal with potentially autoreactive, somatically heterogeneous T lymphocyte receptors. The necessity of maintaining an immunological integrity was the most crucial stimulus for evolution. Thymus as a primary lymphoid organ constitutes an eminent structure that markedly differentiates the higher Vertebrata from the rest of the animal phyla. The present paper is meant to provide a profound evolutionary insight into the lymphoid organs with the emphasis on the thymus morphology through the phylogenesis.

Photoperiodic Modulation in Immune and Reproductive Systems in Japanese Quails (Coturnix japonica): A Morphometric Perspective

“…However, this study revealed that the degree of variation was much higher in the case of primary lymphatic organs as compared to secondary ones. This is consistent with previous findings in which a variation was observed in the regression of primary immune organs in different avian species with some showing more regression compared to others [ 43 ]. The bursal and thymic lymphatic lobules doubled their diameter from the active season to inactive season, while the change in the splenic lobule was only around 75%.…”

The immune system of sturgeons and paddlefish (Acipenseriformes): a review with new data from a chromosome‐scale sturgeon genome

“…In this primary lymphoid and key organ of the adaptive immune system, located in the pharynx of gnathostomes (Boehm & Swann 2014), T cells—named after their origin—are produced and differentiated, thereby playing major roles in cell‐mediated immunity (Boehm et al . 2012a; Mešťanová & Varga 2016). There is a true homology between the thymoids of lampreys (agnathans) and the thymus of gnathostomes (Mešťanová & Varga 2016).…”

“…2012a; Mešťanová & Varga 2016). There is a true homology between the thymoids of lampreys (agnathans) and the thymus of gnathostomes (Mešťanová & Varga 2016). The paired structure and localization of the thymus gland of sharks, sturgeons and teleosts are the same, and because of the homology, their morphology is even similar to that of mammals (Luer et al .…”

Transfer factor treatment in management of peritonitis condition: An experimental study in rat

“…One function of the thymus is to act as the site of maturation of T cells derived from lymphocytes after they have migrated from their place of origin in peripheral lymphoid organs such as the spleen, lymph nodes, and Peyer's patches in the intestine [ 31 ]. If there is thymus deficiency in Wistar rats, there will be no maturation of T cells, so the transfer factor will be unable to increase the activity of macrophages; this is consistent with literature that has shown no clinical and laboratory changes in patients with thymus deficiency following transfer factor treatment [ 32 ].…”