## 4 Discussion
In addition, we confirmed that the 3 Hb extract can reduce observable and quantitative skin damage caused by lipid barrier elimination. As the pH of the SC increases, the activity of LEKTI 1 decreases, leading to the induction of the activity of serine proteases such as KLK7 and an increase in keratinocyte dropout [42]. The activity of the serine proteases activates the G-protein-coupled receptor, which increases the activity of PAR-2 [43]. PAR-2 plays a role as an inflammatory mediator in the skin and is involved in itching and skin barrier homeostasis. The activation of PAR-2 decreases the secretion of lamellar bodies, weakens the lipid barrier, and overexpresses TSLP, which in turn induces Th2 differentiation mediators and allergic inflammatory responses [44]. It can be seen that the inflammatory response is activated through a series of processes that lead to an increase in the pH in the SC. As described above, KLK7, PAR-2, and TSLP cause inflammation through a series of processes. In the 3 HbT group, these processes were considerably inhibited, indicating alleviation of inflammation by the 3 Hb extract. A previous study [45] suggested that normalization of pH in SC is effective in alleviating inflammatory reactions, and hence, the alleviation of inflammation by 3 Hb extract is thought to be due to the normalization of pH in SC. TSLP overexpression increases the secretion of cytokines such as IL-4. IL-4 secretion, in turn, increases the production of B cells, which produce allergen antibodies and induce Th2 differentiation to express CD40L. CD40L binds to CD40 on the surface of B cells, leading to the differentiation of B cells into plasma cells and the production of IgE [27]. IgE induces the activation of mast cells by binding to Fc\(\epsilon\)R on the surface of mast cells [28; 29]. The activation of Fc\(\epsilon\)R induces NF-\(\kappa\)B activity, and IL-4 induces NF-\(\kappa\)B activity [24]. Fc\(\epsilon\)R expression is increased at sites of inflammation [30]. NF-\(\kappa\)B plays an important role in allergic inflammatory reactions by enhancing the production of inflammatory cytokines and chemokines. Therefore, the NF-\(\kappa\)B transcription factor family, which includes p65, plays a central role in the progression and maintenance of AD [31]. Th2 cytokine activity is observed in acute AD lesions [46]. We observed that lipid barrier elimination enhanced Th2 differentiation reaction in LBE group. This leads to acute AD lesions on the skin. In the 3 HbT mice, the decrease in Th2 differentiation could be inferred from the reduction in the number of acute lesions of AD after the administration of the 3 Hb extract. Through a series of processes described earlier, FLG deficiency can cause skin diseases such as AD by inducing inflammatory reactions and Th2 differentiation. We showed that the 3 Hb extract restored FLG. Therefore, 3 Hb extract can prevent a series of processes (inflammatory reactions and Th2 differentiation processes) caused by FLG deficiency. In addition, 3 Hb extract also decreased skin damage in AD. The skin in patients with AD is known to show reduced expression of the components of the skin microenvironment required for maintaining adequate defense. In AD, a decrease in claudin-1 was observed [32], and this decrease caused skin dryness due to an increase in TEWL. The expression of cathelcidin is decreased by Th2 cytokines [33]. TLR is a receptor that is activated when a pathogen is identified and acts as a secondary line of defense against pathogens. Defects in TLR are thought to be a factor leading to AD by potentially allowing bacterial colonization [34]. NHE-1 helps to maintain physiological pH. NHE-1 expression was also found to be decreased in AD [35]. Since FLG gene mutations cause increased skin permeability, it is thought that there is a correlation between FLG deficiency and the skin microenvironment. This study found that in the LBE group, levels of claud, cathelcidin, TLR, and NHE were lower than those in the Ctrl group.