The immune system protects the human body from infections by a series of pathogen (bacteria, viruses, fungi, parasites) [5]. A self-tolerance system prevents the immune response from damaging human tissues. The immune system is always active, carrying out surveillance. The defense to first exposure to the pathogen is represented by two complementary and cooperating functional divisions, the innate immune and, on the other hand, the adaptive immune response, that represents a response based on previous exposure [6]. The innate immune system is represented by dendritic cells, macrophages and neutrophils, with phagocytic activity, and by eosinophils, mast cells and natural killer cells, which release specific soluble antimicrobial factors. The innate immune system includes physical barriers, represented by interconnected epithelial cells (e.g. tight junctions and cellular interactions mediated by cadherin), epithelial cilia and the mucus layer of the respiratory, gastrointestinal and genitourinary epithelium. Moreover, soluble proteins and small bioactive molecules such as complement proteins, defensins and ficolins 1-3, pro-inflammatory cytokines, chemokines, lipid mediators of inflammation, membrane-bound receptors and cytoplasmic proteins are part of the innate immune system. Both innate and adaptive immunity is mediated by leukocytes. Lymphocytes circulate between the blood system and the lymphatic system, passing through the peripheral lymphoid organs, which includes the spleen, tonsils, appendix, lymph nodes and gut-associated lymphoid tissue (GALT). From a common lymphoid progenitor, four major populations of mature lymphocytes are derived, that belong to the adaptive immune system: of B lymphocytes (B cells) and T lymphocytes (T cells), natural killer (NK) cells, and NK-T cells. T-cells can be further categorized to cytotoxic T-cells (TC cells), helper T-cells (Th) and suppressor T-cells. The specific antigenic receptors of the adaptive response are represented by genes that code for an intact T cell receptor (TCR) and immunoglobulin genes (B cell antigen receptor; Ig). TCR is capable of binding the antigen processed by antigen-presenting cells (APC). Dendritic cells represent the most powerful class of APC, and express molecules of the major histocompatibility complex (MHC) of class I and II, necessary for the recognition of the antigen processed by TCR on T cells [7].