Functions of carotenoids in the immune system

Carotenoids act as free radical scavengers that quench the free radicals produced during metabolic activities and immunological functions [1-2]. Acquired immunity is primarily composed of lymphocytes that are themselves capable of killing pathogens or self cells using means such as generating reactive oxidative products (ROS) or aid such lymphocytes to perform their functions adequately. But reactive species do not differentiate between self and non-self hence as a defense mechanisms, such cells utilizes antioxidant molecules to quench oxidants effectively and safe guard the "self" cells. The most widely used dietary antioxidants include vitamin E, vitamin C, carotenoids, flavanoids, zinc and selenium. Carotenoids are also known to play a major role in signal transduction, gene regulation, and disease etiology [3-5]. It boosts the immunity of the vertebrates by stimulating effector T-cell function, enhancing macrophage and cytotoxic T-cell capacities, and also T- and B-lymphocyte proliferation. It has been also found to have immuno-enhancing effects in mammals [6-9]. Apart from it, other major functions which have been reported for carotenoids are:

(i). Quenching reactive species formed by immunoactive cells and immunosuppressive peroxides
(ii). Helping to maintain membrane receptors essential for immune functions
(iii). Aiding the release of immunomodulatory lipid molecules as prostaglandins and leukotrienes
(iv). Reduce or inhibited mutagenesis and inhibit cell transformations
(v). Enhance immune competence and in vitro gap junction communication [10-16].

Beta carotene, lutein and Astaxanthin have showed immunodulating properties. However, Asthaxanthin has showed the better immunodulating action [17] and it is also known for its enhancement of antibody production to T-cell dependent antigen [18]. In 1995, Dr. Jyonouchi et al, showed that astaxanthin enhances human immunoglobulin production in response to T-dependent stimuli even [19]. Astaxanthin also showed anti-microbial activity against H. pylori by shifting the Th1 response towards a Th2 T-cell response [20]. Carotenoids also known for cytokine inducing activities with Astaxanthin showing highest activity, canthaxanthin showed moderate effect while beta carotene with some effect at high doses [21]. In comparision with beta carotene and other carotenoids, astaxanthin is the highest known with its anti tumor activity [4].Other immunological activities of Astaxanthin are: activation of lymphocyte cytotoxic activity; Stimulation of lymphocyte proliferation ; Activation of antibody producing B-cells ; Produces increased number of T-cells; Amplification of natural killer cell cytotoxic activity; Enhanced delayed-type hypersensitivity response ; Dramatically decreases DNA damage[4]. Astaxanthin also consist of anti-inflammatory properties thereby improving the immune health. Astaxanthin suppress different inflammatory mediators eg. Tumor necrosis factor alpha (TNF-a), prostaglandin E-2 (PGE-2), interleukin 1B (IL-1b), nitric oxide (NO),Cox-2 enzyme and nuclear factor kappa-B[22]. Hence, astaxanthin can be used as supplement for the prevention of cancer as it has immune enhancing effects and also can be used for the treatment of inflammation.

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