CD4 and lymphopenia: Vaccines containing the original strain of CPV-2 seem to give protection against the variant CPV-2b, showing that it prevents an increase in acute phase proteins (α-1 acid glycoprotein and serum amyloid A), lymphopenia, neutropenia, and a reduction of the levels of neutrophil-CD4 expression when experimental dogs were inoculated orally and intranasally with a strain of CPV-2b after the application of three doses of a conventional modified live CPV-2 vaccine at 6, 9, and 12 weeks of age [38].