Monocytosis and Lymphopenia in Experimental Rabbit-Pox

During the course of an investigation of a spontaneous epidemic of rabbit-pox,1, 2observations were made on the blood picture of the experimental disease. Standardized pipettes and the supravital technique were employed in making the blood examinations. Striking quantitative changes were noted in two classes of cells. During the height of the disease there was a marked decrease in the number of lymphocytes and an enormous increase in the number of circulating monocytes.In a group of 12 animals systematically studied, the lymphocytes fell from a mean preinoculation level of 2473 or 35.1% of the total count to 847 or 7.5% on the third day following intratesticular inoculation. This was an actual decrease of 65.8% or a relative decrease of 78.6% from the preinoculation lymphocyte level. Simultaneously monocytes rose from a preinoculation value of 374 (5.4%) to 1534 (12.4%) on the third day following inoculation, an actual increase of 310%, or a relative increase of 185% from the mean preinoculation finding. The total white count rose from a mean preinoculation level of 6,971 to 12,530 on the third day. The extreme potency of the virus is evidenced by the fact that 5 of the 12 animals died on the third day after inoculation, and all were dead on the fifth day.Single observations were made on a large number of animals presenting a milder, more chronic form of the disease. Similar changes were observed. Lymphocyte values of less than 1000 per cm. and monocyte counts of more than 3000 were not uncommon. In relative per cent, the lymphocytes frequently composed less than 8% of the total count while monocytes sometimes rose to 40 and 50%.Attention has been called to the monocyte-lymphocyte ratio in tuberculosis3and syphilis.4