Biologia futura: embryo–maternal communication via progesterone-induced blocking factor (PIBF) positive embryo-derived extracellular vesicles. Their role in maternal immunomodulation

Paternal antigens expressed by the foetus are recognized as foreign. Therefore,—according to the rules of transplantation immunity—the foetus ought to be “rejected”. However, during normal gestation, maternal immune functions are re-adjusted, in order to create a favourable environment for the developing foetus. Some of the mechanisms that contribute to the altered immunological environment, for example, the cytokine balance and NK cell function, with special emphasis on the role of progesterone and the progesterone-induced blocking factor (PIBF) will be reviewed.

Mechanisms of immune regulation and transplantation immunity in corneal transplants

At the present time, corneal transplantation (keratoplasty) is one of the most frequent modes of solid tissue transplants in the world. Unlike other kinds of transplants, corneal grafting is often performed without tissue typing and systemic immunosuppression.High frequency of transparent corneal engraftment (up to 90% of cases) in the absence of risk factors is due to special immunoprivileged area in the anterior eye segment (functionally, a structural aggregation of the cornea and anterior chamber, AC) accomplished by local and systemic immunoregulatory mechanisms, i.e., phenomenon of immune deviation associated with anterior chamber of the eye (ACAID), components of the internal liquid medium, a watery moisture with immunosuppressive properties, e.g., IL-1ra, TSP-1,TGF-β2, regulatory complement proteins, α-MSH (alpha-melanocyte stimulating hormone), VIP (vasoactive intestinal peptide), indolamine 2,3-dioxygenase (IDO), calcitonin-gene-bound peptide (CGRP), somatostatin, etc.In addition to ACAID and liquid AC components, a contribution to the maintenance of immune privilege which is extremely important for a successful outcome of keratoplasty, is provided by other mechanisms, in particular, immunologically active membrane-associated molecules of corneal endothelium, i.e., PDL-1 (Programmed death ligand 1), and sVEGFR-1, sVEGFR-2, sVEGFR-3 involved in maintaining avascularity of the corneal tissue. Disturbances of the immune privilege of the cornea promotes activation of immune recognition with switching the effector mechanisms of transplantation immunity, thus leading to subsequent development of the tissue incompatibility reaction and clouding of transplanted cornea. Graft rejection can be localized in any of the corneal cell layers, including epithelium, stroma, and endothelium. Endothelial rejection causes the most severe affection of visual functions, due to the inability of local endothelial recovery, and water accumulation due to the endothelial dysfunction.Graft rejection is clinically characterized by edema and the presence of inflammatory cells, either circulating in the anterior chamber, or forming precipitates on the graft endothelial cells.A number of factors are associated with an increased risk of corneal graft rejection, including the degree of inflammation and/or vascularization of the transplant bed i.e., location of the donor cornea, repeated keratoplasty, allosensitization due to other cellular transplants, including bone marrow, blood transfusions, pregnancy, etc., as well as allergic and systemic diseases.This review article considers and systematizes the data from the literature concerning studies of the factors determining the immune privileged state of cornea, and the ACAID phenomenon, their role in development of allotolerance in corneal transplantation, highlights the main conditions required for triggering the tissue incompatibility reactions, discusses the mechanisms of allogeneic recognition and effector stage of the immune response, destruction of corneal allografts.

Medawar's legacy to cellular immunology and clinical transplantation: a commentary on Billingham, Brent and Medawar (1956) ‘Quantitative studies on tissue transplantation immunity. III. Actively acquired tolerance’

‘Quantitative studies on tissue transplantation immunity. III. Actively acquired tolerance’, published in Philosophical Transactions B in 1956 by Peter Medawar and his colleagues, PhD graduate Leslie Brent and postdoctoral fellow Rupert Billingham, is a full description of the concept of acquired transplantation tolerance. Their 1953 Nature paper (Billingham RE et al . 1953 Nature 172 , 603–606. ( doi:10.1038/172603a0 )) had provided initial evidence with experimental results from a small number of neonatal mice, with mention of similar findings in chicks. The Philosophical Transactions B 1956 paper is clothed with an astonishing amount of further experimental detail. It is written in Peter Medawar's landmark style: witty, perceptive and full of images that can be recalled even when details of the supporting information have faded. Those images are provided not just by a series of 20 colour plates showing skin graft recipient mice, rats, rabbits, chickens and duck, bearing fur or plumage of donor origin, but by his choice of metaphor, simile and analogy to express the questions being addressed and the interpretation of their results, along with those of relevant published data and his prescient ideas of what the results might portend. This work influenced both immunology researchers and clinicians and helped to lay the foundations for successful transplantation programmes. It led to the award of a Nobel prize in 1960 to Medawar, and subsequently to several scientists who advanced these areas. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society .