**3. Discussion**

The present study showed that the administration of the sulfated polysaccharide fucoidan improves the symptoms of psoriasis, an immune disorder disease, changes the composition of intestinal microbiota to include high relative abundance of *Bacteroidetes*, and improves the gu<sup>t</sup> environment by increasing the volumes of mucin and IgA.

First, the administration of the fucoidan diet to psoriasis model mice with the *m-Traf3ip2* mutation gradually improved symptoms, and especially significantly improved phenotypes, scratch test scores, and PASI scores, beginning at 21 days until after 56 days. However, *m-Traf3ip2* mice did not show a preference for the fucoidan diet, and mice in the two dietary groups showed no weight difference. In the same period, we showed the alteration of microflora and the production of mucin at the lamina propria of the mucous membrane and of IgA in cecum. *Bacteroidetes* and *Firmicutes*, which comprise more than 90% of all phylogenetic types, are the two dominant bacterial phyla in the human, mouse [23–25], and pig [26] gut. An analysis of fecal microbiota by genome sequences revealed that feeding of fucoidan to *m-Traf3ip2* mice significantly increased relative abundance of the phylum *Bacteroidetes* for all bacteria beginning at 6 days and continuing beyond 56 days compared to the relative abundance in the normal diet mice.

In a comparison between two phylum groups, *Bacteroidetes* and *Firmicutes*, for all bacteria, *Firmicutes* levels decreased from 2 days after the beginning of the experiments and remained low after 56 days; the analysis was performed using quantitative PCR. These results showed that feed intake of fucoidan by *m-Traf3ip2* mice increased the relative abundance of the *Bacteroidetes* phylum and decreased those of the *Firmicutes* phylum. However, the family *S24-7* in the phylum *Bacteroidetes* was decreased in the fucoidan diet group. It was reported that *S24-7* is related to bowel inflammation [27]. A fucoidan diet changes fecal microbiota and may also have anti-inflammatory effects. On the other hand, the fucoidan diet group showed drastically decreased the relative abundance of the phylum *Firmicutes*. *Firmicutes* was reported to have a wide range of both beneficial and harmful effects on autoimmune disorders. The feces of fucoidan diet group showed a significantly lower relative abundance of the phylum *Firmicutes* compared with the growth rate of control diet group. In this study, levels

of two *Clostridiales* families, *Lachnospiraceae* and *Ruminococcaceae*, were decreased in the intestinal microflora of the fucoidan diet group. Especially, fucoidan administration decreased the presence of *Ruminococcaceae Oscillospira* species in the intestinal microbiota. Our results corresponded with those of another microbiota analysis: soluble dextrin fibers altered the intestinal microbiota and reduced proinflammatory cytokine secretion in male IL-10-deficient mice [28]. Some unidentified members of the *Clostridiales* family may be related to the induction of Th17 cells in the small intestine and aid in protection against pathogens. Th17 cell induction is harmful in patients with an autoimmune disorder [29].

The relative abundance of the phylum *Proteobacteria*, family *Desulfovibrionaceae,* was also higher in the fucoidan diet group than in the control group. Glycomacropeptide is a prebiotic that reduces *Desulfovibrio* bacteria, increases cecal short-chain fatty acids, and has an anti-inflammatory e ffect in mice [30]. In the present study, fucoidan was a possible source of *Desulfovibrionaceae* consumption as a source of nutrition. The increased relative abundance of the family *Desulfovibrionaceae* may be related to some improvement in the symptoms of psoriasis in the present study. The analysis suggested that the fecal microbiota of *Bacteroidetes acidifaciens* were drastically increased in fucoidan diet group in this study (data not shown). Species of *B. acidifaciens* promote the expression of secreted IgA in the large intestine [13,31], and members of the genus *Rikenellaceae* are often found in the gastrointestinal tracts of a number of animals [32]. The species of *B. acidifaciens* may be related to the improvement of symptoms of psoriasis. Additionally, levels of the *Bacteroidetes* species *Parabacteroides* was increased in the fecal microbiota of the fucoidan diet group. Intestinal microbiota of the genus *Bacteroides*, as well as those of *Porphyromonadaceae Parabacteroides*, produce antagonistic substances in ecological niches, preventing the colonization and invasion of exogenous bacteria, and might be one of the mechanisms underlying such prevention [33]. In the present study, drastic increase in the volumes of cecal IgA and ileal mucin was observed in the intestines of fucoidan fed *m-Traf3ip2* mice. Interestingly, these increases coincided with the increase in the *Bacteroidetes* population. β-glucans also have distinctive immunomodulatory characteristics [11,34,35]. In children with chronic respiratory problems, short-term oral application of β-glucan a ffects mucosal immunity by stabilizing secreted IgA levels [36]. The present results sugges<sup>t</sup> that fucoidan administration induces the production of IgA and mucin, rearranging the intestinal environment to regulate immune response [37]. In pigs, a laminarin diet a ffects immune function by increasing genes that encode mucin expression, namely, *MUC2*, *MUC4*, IL-6, and IL-8 in the ileum [11]. Laminarin also binds to mammalian non-Toll-like pattern-recognition receptors, such as, dectin-1, complement receptor-3, lactosylceramide, and scavenger, thereby stimulating innate immunity through the activation of macrophages, dendritic cells, neutrophils, natural killer cells, and helper T-cells [35]. Our study did not elucidate the relation of administration of fucoidan and its molecular action in psoriasis model mice. It will be necessary to elucidate the mechanism underlying the e ffect of fucoidan on the remission of psoriasis.

In conclusion, fucoidan as a dietary supplement could modulate the fecal microbiota composition and repair intestinal barrier function. This study suggested that fucoidan can be used to improve the symptoms of psoriasis.
