Fae

Mature DC

-; Negative response

-; Negative response

Innate immune response Primitive immune response Adaptive immune response

FIGURE 10.4 Innate and adaptive responses in mucosal immunity

FAE; Follicle-associated epitherium, DC; Dendritic cell, TLR; Toll-like receptor, CCR; Chemokine receptor as the first line of immune defense, for example agglutination of micro-organisms; neutralization of bacterial enzymes, toxins, and viruses; immune exclusion; blocking adherence of bacteria to the epithelium; and reduction of antigens or allergen absorption.20 The intestine is the largest single immune organ; it consists of more than 200 m2 of mucosal surface available for antigen uptake and contains more than 70% of an organism's plasma cells. An organism produces more IgA than the organism's production of IgG.20,21

The mucosal immune system evolves mechanisms that can discriminate between harmless antigens, commensal microorganisms, and dangerous pathogens. The ability of the system to distinguish between "dangerous" and "nondangerous" agents is essential for mounting protective immune responses.22 The lymphoid follicles associated with mucosa house two types of dendritic cells; a subpopulation of immature dendritic cells located in close contact with the follicles-associated epithelium (FAE) and a subpopulation of mature, differentiated dendritic cells present in the interfol-licular region associated with T cells (Figure 10.4). Following the antigen processing, primitive or early immune response is induced within several hours after infection in association with NK, yST, CD5+B cells and others, and then antigen-specific adaptive immune response is induced several days later. Dendritic cells process the antigen and present it to T cells in the form of peptides bound to the expressed major histocompatibility complex (MHC) molecules. ILs-7 and -15 secreted from epithelial cells work as cytokines that enhance the proliferation and differentiation of intraepithelial lymphocytes (IELs) and other cells such as dendritic cells for innate and primitive immune responses. "Nondangerous" or harmless antigens like food are presented to T cells by immature dendritic cells that express costimulatory molecules in low levels. Production of IL-10 and TGF^ leads to activation of regulatory Tr-1 or Th3 cells, which in turn inhibits the immune response and induces "oral mucosal tolerance." "Dangerous" antigens like pathogenic microorganisms, on the other hand, induce the maturation of dendritic cells, which express the surface costimulatory molecules such as CD80/86 antigens and produce IL-12 for activation of Th1 cells followed by acquired positive response.

We then investigated antibody responses of IgA and other classes, such as IgE and IgG1, as possible evidence of the protective effects of Spirulina toward food allergy and microbial infection.23 In this study, antibody productions were monitored in mice treated with a hot-water extract of Spirulina, SpHW concurrently or protectively ingested with oral administration of crude shrimp extract as an antigen. Soy- and shrimp- extract antigens had been known to induce IgE antibody response significantly following serial oral injection in C3H/HeJ mice.24 In a primary experiment, ingestion of Spirulina extracts alone did not increase the basal of IgE antibody up to 5 weeks.

Effect of Concurrently Ingested SpHW with Antigen Administration

We first observed antibody levels in the blood and intestinal contents of the mice treated with SpHW concurrently ingested with antigen administration of shrimp (Figure 10.5). Concentrated and diluted SpHW (SPC and SPD) solutions were prepared by dilution of SpHW to 15- and 60-fold, respectively, and were given to Ag-SPC and Ag-SPD groups aseptically. Ag group was given sterilized water. The groups were immunized intraperitoneally with a mixture of crude shrimp extract and inactivated Bordetella pertussis adjuvant as primary immunization followed by oral administration of crude shrimp extract twice a week through an animal feeding catheter for 5 weeks.

Total IgA level in the intestine of Ag group that was orally immunized with antigen alone was almost the same as that of normal nonimmunized animals. IgA antibody levels in the intestine of the Ag-SPD group that concurrently ingested SPD with antigen administration were significantly higher than that of Ag group (Figure 10.6A). Antigen-specific IgE level that was increased in the Ag group, however, was not further enhanced by Spirulina concurrently ingested with antigen, as shown in the Ag-SPC and Ag-SPD groups in Figure 10.6B. Spirulina seemed to neither induce nor enhance allergic reaction such as food allergy dependent on an IgE. IgGl antibody increased by oral administration of shrimp antigen, on the other hand, was further enhanced by the treatment of Spirulina extract in Ag-SPD group (Data not shown).

Effect of Protectively Ingested SpHW Before Antigen Administration

The enhancement of IgA antibody production in the intestine by Spirulina extract was further confirmed. In this experiment, SPD was protectively given to both SPD and SPD-Ag groups for 4 weeks before and for 1 week after primary immunization

Sterilized water

Ag-SPD;

Ag-SPC;

1.1 SPC (15-diluted SpHW)

I-1 : Sterilized SPD (60-fold diluted SpHW)

I-1 Sterilized SPC (15-fold duluted SpHW)

j| : Primary immunization with 400 ^g of shirmp and inactivated Bordetella pertussis (1 x 1010 cells/0.5mL) as an adjuvant, ip injection | Crude shrimp (1.0 mg/mouse), po twice a week Collected blood and intestinal samples

FIGURE 10.5 Concurrent ingestion of Spirulina extract, SPC and SPD, with crude shrimp antigen administration

Five mice per group were used in the experiment.

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