Basic concepts of swine immune system

Innate Immunity

Innate immunity is the first defense barrier against a pathogen or exposure to “foreign” material. If the natural immune barrier (skin, mucous membranes, …) are exceeded, another nonspecific defense response is initiated, which involves the activation of cells of the innate immune system (macrophages, NK cells, dendritic cells…)

Most infectious agents induce an inflammatory response by activating the innate immune system. Some of the cells are as follows:

  • Neutrophils: - recruited from the blood at the site of infection, neutrophils phagocyte and destroy the pathogens. They disappear in 24-48h.
  • Macrophages: they phagocyte and destroy the pathogens, besides they may produce some cytokines and act as antigen presenting cells.
  • Natural Killer cells (NK): they recognize and destroy infected cells by intracellular pathogens.
  • Dendritic cells: following activation by cytokines, they act as antigen presenting cells. At the same time, they produce cytokines that play a role in the differentiation of lymphocytes T helper (Th).

Acquired Immunity

The acquired immunity is divided into humoral immunity and cellular immunity.

In this case it is a specific response against a given antigen and requires a time to activate the cells that will recognize that specific pathogen.

In acquired immunity, there are several types of cells as follows:

  • T helper cells (Th): : these are considered the most important cells in specific immune response; they regulate it. Depending on the type of lymphocytes, they produce one or more cytokines, which leads to different types of immune response. There are several types of lymphocytes, including:
    • Th1: lymphocytes responsible for cellular immunity against intracellular infectious agents. The most relevant cytokines are IFNy and IL-2.
    • Th2: lymphocytes responsible for humoral immunity (antibody production). They help lymphocytes B. The most relevant cytokines are IL-4 and IL-10.
  • B cells: once activated, they secrete antibodies (Ig).
  • Cytotoxic T cells: they act against target cells (infected or tumoral) and they are also involved in the “memory” phase.

Th1 and Th2 cells inhibit each other. A Th1 dominant response vs a Th2 response could modify the result of an infection or challenge.