Research on cytokines is a valid tool for the study of the immune system as they are crucial for regulations of its correct function, being substances that regulate the transfer of information between cells thanks to the activation of membrane receptors.

Moreover, these results [33] confirm that during aging, there is a remodeling of the network level profile of cytokines produced by T helper cells (Th) in our physiological system, which is essential in the correct regulation of the immune system. Moreover, variations of the relationship between the levels of pro- and anti-inflammatory cytokines regulate the immune response which could influence the longevity and the healthy state during aging.

For these reasons, the analysis of the network level profile of the cytokines is a useful tool to define the prognostic biomarkers for aging [8, 9, 33–35]. In this area, results of recent studies [35–37] are relevant which indicate, for the first time, that the immune response is regulated by cytokines that differ between men and women, attributable to these dissimilarities the different trend, between male and female genders, of (1) the immune response, (2) the susceptibility to diseases, and (3) the therapeutic response, opening a new area for the translational research at this level. This study has shown that the gender dimorphism in the Th cytokine pathways is normally present in the regulation of the immune response homeostasis of the healthy state: the antigen-presenting cell (APC) regulates the differentiation and the homeostasis of different Th cell types in rest state and during activation of the immune system of both sexes, but this effect is exerted through Th cytokine pathways specific for each gender (gender-specific) but also through pathways that are common for both (gender-common).

These results [35–37] show, in fact, that the IFN-γ cytokine regulates the male immune system, while IL-6 cytokine regulates the female immune system. The correct functions of the IFN-γ in men and IL-6 in women are biomarkers for the ascertainment of a healthy state of the immune system and then of a healthy longevity. It has been shown, in fact, that an altered functioning of these pathways is a prognostic biomarker for the passage from a healthy condition to the genesis of an adenoma and the progression to a colorectal tumor [35]. On the other side, correct functioning of the IL-10 cytokine regulates the return of the immune system to the rest state, after the response, both in men and women, and, for this reason, it is a prognostic for a healthy longevity in the both sexes but only if IFN-γ in men and IL-6 in women are correctly functioning. If this condition is not respected, IL-10 is a biomarker for the progression of the tumor [30] both in men and women. These results have also revealed that [35] (i) the immune cell production of IL-6 in women and IFN-γ in men decrease during aging; (ii) the age could be a significant and independent factor for the pathways of IFN-γ and IL-10 in men (iii) and for the pathways of IFN-γ and the soluble molecule of the IL-6 receptor (sIL-6R, that modulate the action of IL-6) in women [38].

It has been shown that variations between pro- and anti-inflammatory cytokines could influence the success of the immune response [33–35]. However, the most relevant discovery for the definition of these suitable prognostic biomarkers is the identification of “double prognostic biomarkers”: they are constituted by couple of pro- and anti- inflammatory cytokines that differ between men and women and assure the success of the immune response varying in appropriate correlation with each other [35, 36] and following different pathways in each gender.

These results [35, 36] have been shown that the early evolution of the immune response is influenced by the positive correlation between the production of IFN-γ―IL-10 and IL-6―IL-4 in men and the negative one between IL-6―IL-10 in women. The evolution of the late response is also influenced by the positive correlation between the production of IFN-γ―IL-4 in men and IL-6―IFN-γ in women. More specifically, the “double prognostic biomarkers” for men are related by direct proportionality (they both increase or decrease together with the same trend, both positive or negative) between the IFN-γ―IL-10, IL-6―IL-4, and IFN-γ―IL-4 cytokine levels, while they are interconnected in women by an inverse proportionality (an increase of the first correspond to a decrease of the second and vice versa) between the IL-6―IL-10 cytokine levels and with a direct proportionality between IL-6―IFN-γ cytokines (Fig. 3.4). These variations between the couple of inflammatory and anti-inflammatory cytokines, specific for each gender, are to be considered “double biomarkers” gender-specific, in the valuation of relationships (1) between aging and a healthy longevity, to define the a and b types of indices, respectively of no and of low risk of pathology, for the healthy population prevention; of no and of low therapeutic risk for a better treatment selection of tumor patients; (2) between aging and pathology, to define the indices of c type with a high- risk of pathology for the healthy population prevention and a high therapeutic risk, for tumor patient treatments.

The relevance of the gender-specific differences in the regulation of the immune response is underlined by the evidence that homeostasis is preserved and there are no differences between men and women in the outcome of this response when the pathways of the gender-specific cytokines (IFN-γ e IL-6) still normally work [35, 36]. When alterations occur in the pathways of the gender-specific cytokines, the consequences for men and women are different, in terms of disease development. This event is related to the impairment of the immune system homeostasis, because the alterations of gender-specific cytokine pathways cause a pathologic polarization of specific T-cell types, different for each gender. The reason of this fact is related to the different effects on the generation of Th cell subtypes during the immune response generated by IFN-γ and IL-6 cytokines, present in the cellular environment. IFN-γ sustains the development of the Th1 type [39], while IL-6 supports the Th2-type differentiation and the activation of B-lymphocytes with the related production of antibodies. In addition, research in this area showed that it is not a single cytokine to determine a particular response but the interactions between different individual cytokines, organized in a network. These results [35, 36] indicate that the different predisposition to gender-specific diseases and the related disease progression are related to different cellular gender-specific polarization of the Treg, Th17, and Th9 cells, determined by interactions between TGFβ, IL-6, IFN-γ, IL-10, and IL-4 cytokines that vary between men and women [36]. These results are confirmed by the evidences of other researches that indicate the existence of mutual relationships in the Treg, Th17, and Th9 cells, because (i) TGFβ triggers the expression of Foxp3 transcription factor in naïve T cells, generating Treg cells, but (ii) IL-6 inhibits the TGFβ-driven expression of Foxp3, and TGFβ together with IL-6 induces ROR-gt transcription factor, triggering the developmental program of Th17 cells [36, 40], while (iii) IL-4 also inhibits TGFβ induction of Foxp3 expression, but TGFβ together with IL-4 induces Th9 cells’ differentiation that produce IL-9 cytokine. The co-expression of IL-9 and IL-17 has been identified as a new function of Th17 in the mediation of tissue destruction and of the neurodegeneration [41, 42]. The female greater susceptibility to autoimmune diseases, as multiple sclerosis, could be attributed to the dominant influence of IL-6, in the inhibition of the regulatory cells that play a fundamental role in these diseases [40, 43–45]; the greater male susceptibility to, for example, the primary form of progressive multiple sclerosis (MS) [46] could be the result of the prevalent influence of IFN-γ in the control of Th9 cells that predispose to neurodegeneration. The IL-9 receptor complex is constitutively expressed on the astrocytes, and IL-9 induces the expression on these cells of CCL-20 but not the other chemokines [47], determining the migration of Th17 cells in the CNS where they promote neurodegeneration. Treg, Th9, and Th17 cells have shown to be important in the autoimmune diseases, as rheumatoid arthritis [48] and MS [49].

Results in the research on MS [36] confirm these data, showing that alterations of the IL-6 pathways are involved in the loss of homeostasis of the immune system which is evident in a disequilibrium of Treg cells and in an increase of the neurological deficit in both gender, underlining the autoimmune etiology of MS. Further support of the existence of gender-specific pathways is provided by this study, observing that the benefit of the treatment with IFN-β (in the reestablishment of the immune system homeostasis and in the inhibition of the neurological deficit) is related to the reestablishment of IL-6 pathways in women and IFN-γ pathways in men. Moreover, the serum levels of the soluble molecule sCD30 and of the TGFβ cytokine could be used in both genders as “double biomarkers,” for the assessment of the therapeutic success in terms of reestablishment of the immune homeostasis of the Th cells and the absence of the progression of neurological deficit.

Overall, these results shed light on the necessity of (a) suitable gender-specific biomarkers and (b) gender-specific drugs, whose activity could consider the different regulation system of the immune response between the two genders, assuring the same therapeutic results: return to the physiologic homeostasis thanks to the passage from an activation pathological state to a rest one.

On these bases, it is possible to affirm that the definition of suitable gender-specific biomarkers could lead to new strategies of preventions and to personalized treatments [37].

The redox control of the cellular physiology is one of the most relevant regulatory mechanisms in every living organism. Mammal cells contain two Trx-systems. The first is the Trx1/RTx1 that is normally localized in the cytoplasm but, in stress condition, could migrate into the nucleus (inducing the genetic codification) or it could be secreted in the extracellular environment [78] and, in this way, it attends the immune system network. The second system (Trx2/RTrx2) is localized in mitochondria and in the cytoplasmic reticulum, and it regulates cellular apoptosis [79]. There are two other system: the first is called TRXs testis/sperm-specific and is localized on the spermatids (Sptrx-1, Sptrx-2, and Sptrx3), and the second is the Txl-2 localized in lungs and in other ciliate tissues [80].