Dear Sir,
Based on my study of the data reported by Tetel et al. Research Note: Sex difference in changes in heterophil to lymphocyte ratios in response to acute exposure of both corticosterone and cortisol in the Pekin duck Poultry Science 101:101914. I made the following observations regarding the application of the H/L ratio, a subject in which I have some expertise. The manuscript is published as a “Research Note,” necessitating its adherence to format limitations of Poultry Science, yet some critical methodology descriptions seem lacking. First, neither identity of the “independent lab” where the CBCs were performed, nor the actual CBC data used to compute the H/L ratios were specified. A single data table could have accommodated at least some of this information. Furthermore, no description of the H/L computation itself is provided. Which lymphocytes were used for the denominator, and which granulocytes were in the numerator? What were the total white blood cell counts of the controls and the experimental ducks? Were the statistical models age-adjusted? Were treatment groups of balanced ages?
Figure 1A shows that control hens had H/L ratios of about 3, a value nearly 6 times the stress/nonstress cutoff of 0.5 in wide use. The H/Ls of experimental hens were even more remarkable. Judging by the figure, cortisol treatment resulted in H/Ls above 20 with some near 30. Figure 1B, the results of the experiment using drakes, indicated that some individuals had H/Ls between 10 and 15. These values are extraordinary, likely associated with TWBC beyond leukocytosis and well into leukemoid reaction levels. H/Ls as high as described need to be accompanied by the TWBC data at a minimum.
The described high H/L ratios would likely be associated with an acute inflammatory reaction caused by the treatments, or possibly by a disease outbreak, either of which would result in hemograms having atypical cells of all series.
The authors discuss their findings in the context of species having lymph nodes. Although ducks do have lymph nodes, unlike most other avians, the authors do not mention the prominence (lymphadenopathy) of lymphoid elements that might be expected if heterophils of their reported H/Ls originated from those structures.
The time frame for the hematology study deserves comment, as the drastic H/L effects occurred within 3hr. How would the Arneth profile of the responding heterophils appear? Under such a cellular demand many meso/myelocytes would have been expected to be in the circulation. How would those cells be inserted into the H/L? Where could the responding cells have been kept in reserve? More importantly, why would a duck or any species, not otherwise stressed, maintain the cellular reserves necessary to support H/Ls of 20 to 30?
I suggest that these combined methodological and physiological issues obfuscate the conclusions advanced by these authors.
Sincerely yours,
Paul F. Cotter