It has been suggested that aloe may have immune-stimulating capabilities. Much of the available research has been performed on mice or in vitro and aloe shows antiviral, antitumour and non-specific immunostimulant activity. An experiment in 1980 demonstrated that mice given aloe extract 2 days before exposure to pathogens were protected against a variety of fungi and bacteria (Brossat et al 1981). Later, the isolated compound acemannan (beta-(1,4)-acetylated mannan) was shown to increase the response of lymphocytes to antigens in vitro (Womble & Helderman 1988). In mice, acemannan stimulated cytokines, bringing about an immune attack
on implanted sarcoma cells, leading to necrosis and regression of cancer cells (Peng et al 1991). A later trial investigated the effects of acemannan on mouse macrophages (Zhang & Tizard 1996). Acemannan stimulated macrophage cytokine production (IL-6 and TNF-alpha), NO release, surface molecule expression, and cellular morphologic changes. Similarly, a polysaccharide fraction isolated from Aloe vera promoted human keratinocytes to secreteTGF-alpha, TGF-beta-1, IL-1 -beta, IL-6, IL-8 and TNF, and inhibited the release of NO as compared to control (Chen et al 2005). The immune enhancing effects of acemannan may be due in part to the compound's ability to promote differentiation of immature dendritic cells (Lee et al 2001). These cells are crucial for the initiation of primary immune responses.
Three purified polysaccharide fractions (PAC-I, PAC-II, and PAC-III) from A. vera stimulated peritoneal macrophages, splenic T and B cells, and increased the ability of these cells to secrete TNF-alpha, IL-1 -beta, IFN-gamma, IL-2, and IL-6 (Leung et al 2004). The compound with the highest mannose content, and therefore the highest molecular weight (PAC-I), demonstrated the most potential. A 99% pure carbohydrate compound (purified acemannan) isolated from aloe demonstrated potent haematopoietic and haematologic activity in myelosuppressed mice (Talmadge et al 2004).
Specific manufacturing methods can be applied to enhance the extracts. For example, 1 g of extract obtained from leaves subjected to cold and dark treatment contained 400 mg of neutral polysaccharide compared with 30 mg in leaves not specially treated (Shida et al 1985).
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