Abstract
Dietary food components have the ability to affect immune function; following absorption, specifically orally ingested dietary food containing lectins can systemically modulate the immune cells and affect the response to self- and co-administered food antigens. The mannose-binding lectins from garlic (Allium sativum agglutinins; ASAs) were identified as immunodulatory proteins in vitro. The objective of the present study was to assess the immunogenicity and adjuvanticity of garlic agglutinins and to evaluate whether they have adjuvant properties in vivo for a weak antigen ovalbumin (OVA). Garlic lectins (ASA I and ASA II) were administered by intranasal (50 days duration) and intradermal (14 days duration) routes, and the anti-lectin and anti-OVA immune (IgG) responses in the control and test groups of the BALB/c mice were assessed for humoral immunogenicity. Lectins, co-administered with OVA, were examined for lectin-induced anti-OVA IgG response to assess their adjuvant properties. The splenic and thymic indices were evaluated as a measure of immunomodulatory functions. Intradermal administration of ASA I and ASA II had showed a four-fold and two-fold increase in anti-lectin IgG response, respectively, vs. the control on day 14. In the intranasal route, the increases were 3-fold and 2.4-fold for ASA I and ASA II, respectively, on day 50. No decrease in the body weights of animals was noticed; the increases in the spleen and thymus weights, as well as their indices, were significant in the lectin groups. In the adjuvanticity study by intranasal administration, ASA I co-administered with ovalbumin (OVA) induced a remarkable increase in anti-OVA IgG response (~six-fold; p < 0.001) compared to the control, and ASA II induced a four-fold increase vs. the control on day 50. The results indicated that ASA was a potent immunogen which induced mucosal immunogenicity to the antigens that were administered intranasally in BALB/c mice. The observations made of the in vivo study indicate that ASA I has the potential use as an oral and mucosal adjuvant to deliver candidate weak antigens. Further clinical studies in humans are required to confirm its applicability.
Highlights
Lectins are typical globular proteins of nonimmune origin displaying binding to specific carbohydrates of oligo/polysaccharides, glycoproteins, and glycolipids
The ingested dietary components should pass through the digestive tract, which is the largest immunological organ of the body, where dietary molecules interact with the immune cells
The observations drawn in the present study demonstrated that garlic lectins (ASA I and Allium sativum agglutinin (ASA) II) are effective immunogenic proteins which stimulate humoral antibody (IgG) responses following the systemic and mucosal administration of antigens
Summary
Lectins are typical globular proteins of nonimmune origin displaying binding to specific carbohydrates of oligo/polysaccharides, glycoproteins, and glycolipids. Lectins promote diverse biological consequences and enhance the absorption of dietary co-administered antigens [6,7], and on oral administration, these lectins are capable of inducing specific targeted immune responses to self- and co-administered antigens, which is in contrast to nonfunctional dietary food proteins [8]. Evidence has been exhibited for the dislocation of dietary food lectins across the gut epithelium in both humans and mice [8,13]. This can be exploited for the formulation of a lectin-based oral vaccine-targeted delivery to induce both mucosal and systemic immune responses against weak antigens. Several plant food lectins are known to be mitogens, to activate lymphocytes in vitro [14,15], and to induce high levels of specific anti-lectin serum IgG through the mucosal and oral routes of administration in mice [16,17]
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