Happy turkey Day! Well, to be honest, this particular turkey is not so happy, as you can see from this image from its peripheral blood smear. If you are not familiar with the pictured cell, it is actually a special type of plasma cell known as a Mott cell. Mott cells, named for surgeon F.W. Mott who first identified them in 1905, are characterized by the accumulation of immunoglobulin in packets known as Russell bodies. While normal plasma cells may be seen in peripheral blood in low number in healthy birds and reptiles, the presence of Mott cells in peripheral blood is quite unusual in poultry and almost unheard of in other species! 

The turkey in question presented for left pelvic limb lameness as well as bilateral intertarsal joint automutilation. This presentation parallels findings reported by Cotter, who noted that many poultry with Mott cells in circulation initially present for lameness. Further review of cases involving Mott cells revealed that the majority are associated with bacteremia or fungemia. Mott cells containing intracellular bacteria have even been observed in blood smears from poultry, revealing a phagocytic function in these birds that has not been reported in other species! 

We still have a lot to learn about Mott cells in poultry, as the literature on the subject is limited. One thing we can say for sure, though, is that their presence in peripheral blood is always abnormal and warrants further investigation.

References

Cotter PF. Are peripheral Mott cells an indication of stress or inefficient immunity? Poult Sci. 2015 Jul;94(7):1433-8. doi: 10.3382/ps/pev053. Epub 2015 Feb 27. PMID: 25725075.

Cotter, P. and M. Bakst. “A comparison of Mott cell morphology of three avian species. II. ‐ Bad behavior by plasmacytes?” Poultry Science 96 (2017): 325–331.

Mott FW. Observation on the brain of men and animals infected with various forms of trypanosomes. Preliminary note. Proc R Soc Lond. 1905;76:235–242.

Raskin RE. Lymphoid system. In: Raskin RE, Meyer DJ, eds. Canine and Feline Cytology: A Color Atlas and Interpretation Guide. 2nd ed. St. Louis, MO: Saunders Elsevier; 2010:77–122.