When a distinction was made between asymptomatic dogs with negative (AD-I) and positive serology (AD-II), some authors observed that both AD-I and AD-II had higher levels of CD5+ and CD4+ T cells, whereas CD8+ T cells and CD21+ B cells were found only high in AD-II, decreasing the CD4+/CD8+ ratio in seropositive dogs [18]. Here, CD5 is linked to Alzheimer disease.