Naturally or experimentally-induced protection against T. circumcincta following infection is a complex phenomenon in which several immunoglobulins such as IgA, IgE, IgG, cells such as eosinophils, mast cells, globule leukocytes (GL), CD4+, plasmatic cells and other factors, like IL-4 and/or 5 or galectins are implicated. The gene discussed is CD4; the disease is infection.