Increase in the haemolytic complement activity of dogs affected with cyclic haematopoiesis

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Cyclic haematopoiesis (CH) is an inherited disorder which occurs in both humans and Grey Collie dogs. The disease is characterized by fluctuations in the numbers of peripheral blood leucocytes, reticulocytes and platelets at regular intervals and is associated with a variety of clinical signs. The most prominent cycle observed is that of neutrophils. The 12-day neutropenic cycle includes a period of relatively normal neutrophil counts, a period of neutropenia and generally a period in which neutrophil counts greatly exceed the normal range. In this study the daily serum haemolytic complement activity (classical pathway CH 50) of CH and normal Collie dogs was assayed. The serum CH 50 of normal Collie dogs was relatively stable throughout the test period. In contrast, the serum CH 50 of CH dogs fluctuated extensively and the mean serum CH 50 of CH dogs during the neutropenic cycle greatly exceeded that of normal Collie dogs over the same test period. A close temporal relationship between the stage of the CH neutropenic cycle and the serum CH 50 was observed. The mean serum CH 50 during neutropenia was not significantly different from that observed when neutrophil counts were within normal range, both values being significantly higher than that of normal dogs. However, the mean serum CH 50 during the period of neutrophil rebound was significantly (P<0.01) higher than that during the period of neutropenia or normal neutrophil counts. These data suggest that alterations in the production of complement components or regulatory proteins occur at regular intervals in CH dogs.