ZAP-70 and Syk expression in canine lymphoid cells and preliminary results on leukaemia cases

Zeta-chain-associated protein (ZAP-70) and spleen tyrosine kinase (Syk) are
structurally and functionally homologous tyrosine kinases playing a role in the
T- and B-cell signal transduction. Their activation can lead to lymphokine
production, cytolitic activity, antibody secretion, cell proliferation,
differentiation, survival and phagocytosis. Anomalous ZAP-70 and Syk expression
is reported to be related to tumor formation and progression, and ZAP-70
immunoreactivity is a good prognostic marker of disease progression in human
chronic lymphocytic leukaemia (CLL). Until now, to our knowledge, there are no
reports about canine ZAP-70 and Syk expression profiles. In the present study, a
RT-PCR procedure for the quali-quantitative evaluation of canine ZAP-70 and Syk
transcripts was designed. The expression patterns of canine ZAP-70 and Syk mRNAs
were evaluated in canine leukocyte subpopulations and in peripheral whole blood
samples from healthy dogs and from dogs with different types of leukaemia.
Similarly to humans, normal canine CD4+ and CD8+ T cells showed high expression
of ZAP-70, whereas Syk was abundantly expressed in normal CD21+ B cells. The
expression profile of ZAP-70 and Syk was markedly different in canine normal and
leukaemic blood. Decreased Syk expression was detected in dogs with T-cell CLL,
whereas decreased ZAP-70 expression was detected in dogs with B-cell CLL and
B-cell acute lymphocytic leukaemia (ALL). The comparison of ZAP-70 and Syk mRNA
levels between normal and leukaemic peripheral whole blood showed that the
expression ratio ZAP-70/Syk is subjected to modification depending on the
leukaemia status of patients. The results of the present work open an interesting
topic for leukaemogenesis investigation and are the basis for further studies for
a proper evaluation of the potential utility of these parameters for the
diagnosis and prognosis of canine T- and B-cell leukaemia.