Prolonged depletion of circulating CD4+ T lymphocytes and acute monocytosis after pantropic canine coronavirus infection in dogs

Abstract

A hypervirulent strain (CB/05) of canine coronavirus was employed to infect oronasally 11-week-old pups. Peripheral blood monocytes (CD14(+)), T lymphocytes (CD4(+) and CD8(+)) and B lymphocytes (CD21(+)) were studied by flow cytometry within 5 days post-infection (p.i.) and at later time points. Infection with CB/05 resulted in a profound depletion of T cells and a slight loss of B cells in the first week p.i. In particular, while the CD8(+) and the B lymphocytes returned to baseline levels by day 7 p.i., the CD4(+) T cells remained significantly low until day 30 p.i. and recovered completely only at day 60 p.i. Monocytosis was also observed after CB/05 infection with a peak at day 5 p.i. The prolonged depletion of peripheral CD4(+) T cells did not alter the levels of serum IgG or IgM. The impact of CB/05 infection on the immune performance of infected pups is discussed.

Fig. 1

Kinetics of CD14⁺, CD4⁺, CD8⁺, CD21⁺ peripheral blood cells in dogs (n = 10) infected with the pantropic CB/05 CCoV. Blood was taken 3 and 5 days following the infection and the absolute numbers of cells were measured by flow cytometry. Data are expressed as the arithmetic mean ± S.D. Asterisks indicate statistical significance (p < 0.05) between the indicated absolute count value and the baseline value (i.e., day 0).

Fig. 2

Kinetics of CD14⁺, CD4⁺, CD8⁺, CD21⁺ peripheral blood cells in dogs infected with the pantropic CB/05 CCoV. Blood was taken until day 24 p.i. (n = 4) or day 60 p.i. (n = 2) and the absolute numbers of cells were measured by flow cytometry. Data are expressed as the arithmetic mean ± S.D. Asterisks indicate statistical significance (p < 0.05) between the indicated absolute count value and the baseline value (i.e., day 0).

Fig. 3

Paraffin-embedded histological sections stained with H&E, 10×; (A) damage of the epithelium and infiltration of the lamina propria by lymphocytes and plasma cells in the duodenum; (B) severe lymphoid depletion in mesenteric lymph nodes.