Novel Aspects in Immunodeficiencies

This thesis reports the results I obtained during my PhD course in “Human Reproduction, Development and Growth” (XXII Cycle) from 2006 to 2009. The field of the clinical description, genetic characterization, and immunological investigation of novel PIDs, born in the 1950s, in the last twenty years of the 20th century has revealed a formidable numbers of scientific discoveries. Many scientific papers have been published on the molecular and cellular basis of the immune response and on the mechanisms involved in the correct ontogeny of immune system components. Although today we know the genetic and molecular basis of those principal mechanisms involved in the immune response, this field retains a great potential for growth. During the three years of my PhD program I have contributed in some measure to clarify some “Novel aspects in Immunodeficiencies”, through the combination of clinical, cellular, functional and molecular approaches. In particular, studying a group of atypical patients with X-SCID I contributed to demonstrate for the first time a previously unappreciated functional interaction between the GHR apparatus and the gc. Furthermore, this knowledge helped me to reveal a prior unidentified property of the common gc trasducing element. I could demonstrate, in fact, that this subunit is able to influence the cell-cycle progression, spontaneous or GH-induced, in a concentration dependent manner. Moreover, I spent my PhD also to better characterize at both molecular and clinical levels the human Nude/SCID phenotype. In this context, I could suggest for the first time a functional role of FOXN1 transcription factor in the development and differentiation of the central nervous system. In addition, among those PIDs whose causing genes are not selectively expressed in the hematopoietic compartment, I contributed to the study first of the effects of steroid treatment in patients affected with Ataxia telangiectasia, currently without an effective treatment, and after of the role of oxidative stress in its beneficial therapy. During my PhD I also paid a particular attention to T-cell ontogeny defects affecting both the positive and negative selection processes. In this field I had a unique opportunity to study T-cell development in humans in the absence of a functional thymus; this study led to the identification of some subsets of T-cell able to mature in extrathymic sites. In the context of the negative selection process, I studied the role of peripheral tolerance mechanisms in the high phenotypic intra-familiar variability existing in the APECED syndrome. Overall, all my studies were designed in order to clarify some unknown mechanisms underlying the functionality and the development of the immune system well as to study the basis of some regulatory networks governing the interactions existing between the immune and other systems

Human clinical phenotype associated with FOXN1 mutations.

In humans, a proper immune response relies on the innate immunity, characterized by a rapid and nonspecific initial response to infections, and later on the adaptive immunity, characterized by a specific response to a particular antigen. Disruption of any part of the orchestrated immune response results in the inability to control infections and, subsequently, in illness. An impairment of both effector arms of the specific immunity characterizes the clinical phenotype, known as severe combined immunodeficiency (SCID), which represents a heterogeneous group of inherited disorders due to abnormalities of T, B and NK cells. The first congenital SCID was described as spontaneous immunodeficiency in 1966 in mice and referred as Nude/SCID, based on the association of athymia with complete hairless. In 1996, the human equivalent of the murine Nude/SCID phenotype (MIM #601705) was reported. As in mice, also in humans this form is characterized by an intrinsic defect of the thymus, congenital alopecia and nail dystrophy, and is due to mutations of the FOXN1 gene, as well. FOXN1 is mainly expressed in the thymus and skin epithelial cells, where it plays a critical role in differentiation and survival. FOXN1 belongs to the forkhead box (FOX) gene family that comprises a diverse group of ‘winged helix’ transcription factors involved in development, metabolism, cancer and aging. These transcription factors share the common property of being developmentally regulated and of directing tissue specific transcription and cell fate decisions. In immune system, alterations of FOXN1 result in a thymus anlage that lacks the capacity to generate mature and functional thymocytes. Because the significant expression levels of FOXN1 in skin elements, keratinocytes have been successfully used to support a full process of human T-cell development in vitro, resulting in the generation of mature T cells from hematopoietic precursor cells (HPCs). This finding would imply a role for skin as a primary lymphoid organ. Thus, the present chapter will focus on the information that came out from the original description of the human Nude/SCID phenotype and on the role of FOXN1 and of the other members of FOX subfamilies in those immunological disorders characterized by abnormal T-cell development or abnormal T-cell regulatory homeostasis

Experimental observations and theoretical interpretation of the mechanical behaviour of a grouted pyroclastic silty sand

This paper deals with the mechanical characterisation of an artificially structured material, obtained by grouting a low permeability pyroclastic silty sand (pozzolana) with a sodium silicate solution. Notwithstanding the low permeability of pozzolana (k(sat) = 10(-6) divided by 10(-7)m/sec), a preliminary set of laboratory tests has shown that the very diluted silicate grouts adopted are effective in enhancing its mechanical behaviour. The paper refers on a detailed experimental programme carried out to investigate the stress-strain behaviour of the grouted soil in order to outline its peculiar mechanical properties. With this aim, oedometer, CID and CIU triaxial tests were carried out. The whole set of results shows the typical behaviour of a structured material, with a brittle behaviour at low stress levels, and structural degradation at higher stresses. A first attempt to explain the experimental observations is proposed in the light of the classical Critical State Soil Mechanics theory and some preliminary conclusions are discussed

La Sindrome Nude/SCID: dal modello murino al fenotipo umano

A proper normal immune response is initially based on the innate immunity, characterized by a rapid and nonspecific response to infections, and later on the adaptive immunity, characterized by a specific response to a particular pathogen. Disruption of any part of the orchestrated immune response can result in an inability to control infections and subsequent illness. Primary immunodeficiencies are congenital disorders of the immunological response, which can be divided into subgroups on the basis of the component of the immune system predominantly affected, including T, B, NK lymphocytes, phagocytic cells and complement proteins. The severe combined immunodeficiency (SCID), characterized by abnormalities of T, B and NK cells, consists of a group of distinct diseases associated with a severe clinical phenotype due to an impairment of both effector arms of the specific immunity. In the 1996, a novel form of SCID (MIM 601705; Pignata guarino syndrome) was described, and proposed as the human equivalent of the well known murine phenotype described by Flanagan in 1966. This murine model was defined as Nude/SCID. The hallmarks of the Nude/SCID phenotype are congenital alopecia, from which the term “Nude” for the spontaneous murine model, nail dystrophy and an intrinsic defect of the thymus, always associated with a profound T-cell defect. The affected mice described by Flanagan, also showed an inborn dysgenesis of the thymus resulting in a compromised immune system lacking T cells. Moreover, molecular studies on the nude murine model led to identify Foxn1 as the gene responsible of the Nude phenotype. Also in humans as in mice, the molecular analysis reveals alterations in FOXN1 gene. Of note, the immunological phenotype of these patients is characterized by a marked reduction of CD3+, CD4+ and CD8+ cells and by the absence of naïve CD4+CD45RA+ cells. It should be mentioned that studies performed in Nude/SCID mice gave a great contribution to the knowledge of cell-mediated immunity. In humans for a long time, the DiGeorge syndrome (DGS) was erroneously considered the human counterpart of the murine Nude/SCID phenotype. However, because of the profound differences among DGS and mouse Nude/SCID, the mouse model has been considered misleading to understand T-cell ontogeny in humans. The description of the human equivalent of the Nude/SCID syndrome unravelled many of the dilemmas of T-cell ontogeny in man. Novel knowledge in this field would be very helpful in the comprehension of the intimate mechanisms underlying the T-cell differentiation process in humans and in discovering novel clinical entities related to abnormalities of the process