These observations are often a characteristic feature of the development of PID, including a decrease in the number of T lymphocytes and a decrease in the CD4 to CD8 ratio (this ratio is reduced even to <1), as well as a reduced number of B lymphocytes; these changes may indicate an impaired response of the body to all kinds of infections that often accompany PID, including patients with CVID. Here, CD4 is linked to common variable immunodeficiency.