**1. Introduction**

Dinoflagellates are unicellular phytoplankton and are known to produce various bioactive secondary metabolites [1–6]. The genus, *Symbiodinium*, which belongs to the zooxanthellae, is a representative symbiont found in many marine invertebrates. They also produce unique and complex bioactive secondary metabolites [1,2,4] together with a peridinin. Peridinin is one of the carotenoids that is synthesized in dinoflagellates. 

Carotenoids have numerous bioactivities. In particular, the marine carotenoid, fucoxanthin, has multiple functions and has been reported to have considerable potential for applications for improving human health [7–12]. For example, fucoxanthin induces the uncoupling of protein 1 expression in white adipose tissue mitochondria [7]. It also improves insulin resistance and decreases blood glucose levels [7]. Kim *et al.* [9] reported that fucoxanthin reduces the levels of proinflammatory mediators, including NO, PGE2, IL-1 Ά, TNF- ΅ and IL-6, via the inhibition of NF-ΎB activation and the suppression of MAPK phosphorylation in leukemic monocyte RAW264 cells. Sakai *et al.* [8] reported that fucoxanthin, astaxanthin, zeaxanthin and Ά-carotene significantly inhibit the antigen-induced release of Ά-hexosaminidase in basophilic leukemia 2H3 and mast cells and that these carotenoids 

also inhibit antigen-induced aggregation of the high affinity IgE receptor on mast cells. Further, 

Sakai *et al.* [10] reported that these carotenoids inhibit dinitrofluorobenzene-induced contact hypersensitivity in the ears by reducing the TNF- ΅ and histamine levels in the ear. 

In contrast, the bioactivities of peridinin, which has a structure similar to that of fucoxanthin 

(Figure 1), have not been well studied. Tsushima *et al.* [13] reported that peridinin has a strong inhibitory effect on Epstein–Barr virus early antigen activation in Raji cells at a lower concentration, but shows cytotoxicity to Raji cells at a higher concentration. Sugawara *et al.* [14] reported that peridinin induced apoptosis of human colorectal cancer cells by activating both caspase-8 and caspase-9. 

**Figure 1.** Chemical structures of peridinin and fucoxanthin. 

Here, we examine the bioactivity of peridinin as a functional material for human health. Recently, the number of allergy sufferers has increased worldwide. In this paper, we examined the inhibitory effect of peridinin on delayed-type hypersensitivity in mice and compared it with that of fucoxanthin. 

## **2. Results and Discussion**

## *2.1. Effect of Peridinin on DTH in BALB/cAJc1 Mice*

Eosinophils are well-known granulocytes that increase at the sites of inflammation as part of the delayed-type hypersensitivity (DTH) response. Eosinophils are reported to increase in response to picryl chloride (PCl; 2,4,6- trinitrochlorobenzene) in BALB/cAJc1 mice [15]. In that study, treatment with cyclophosphamide 2 days before sensitization resulted in marked blood and tissue eosinophilia. We applied the same experimental protocol to elicit the DTH response. 

Hydrocortisone strongly suppressed the DTH response at 24 and 48 h (22.4% and 18.2% suppression, respectively; Figure 2) after the antigen challenge. Peridinin also suppressed the DTH response in BALB/cAJc1 mice, both at 24 or 48 h after the antigen challenge by both routes of administration, painted onto ears (paint) (8.9% and 9.2% suppression, respectively; Figure 2) or administered intraperitoneally (i.p.) (12.7% and 11.7% suppression, respectively; Figure 2). In contrast, fucoxanthin did not suppress the DTH response at either 24 or 48 h after the antigen challenge (Figure 2). 

Increased ear thickness is caused by the accumulation of lymphocytes, macrophages, neutrophils and eosinophils. Furthermore, macrophages stimulate the proliferation of fibroblasts. The accumulation of these cells to the site of antigen challenge results in the increase of ear thickness. It is suggested that peridinin reduced at least one of these factors. We focused on eosinophils, because they are typical white blood cells that increase in allergic reactions. 

positive control group.
