T lymphocytes play a crucial role in the development of protective immunity against intracellular pathogens. Studies on mouse CD4c T cell clones showed that helper T (Th) cells can be divided into Th1 and Th2 subsets based on their cytokine production. Interleukin- 4 (IL-4) is a cytokine produced predominantly by the Th2 subset. It is involved in stimulation and class switching of B cells, acts as a growth factor for Th2 cells, and inhibits Th1 type of reactivity (Mosmann et al. 1987). In mice resistance and susceptibility toLeishmania infection were highly correlated with predominance of Th1 and Th2 reactivity, respectively (Locksley and Scott 1991). We study the immune responses in dogs infected with Leishmania infantum. Protective immunity in canine visceral leishmaniosis (CVL) is associated with a Th1 type of response (Pinelli et al. 1994, 1995). Our knowledge of CVL would greatly benefit from the development of dog Th2 specific reagents. This paper reports the cloning and sequencing of cDNA containing the coding sequence of dog IL-4 performed by the rapid amplification of cDNA ends (RACE) protocol (Frohman 1995). For this purpose mRNA isolated from concanavalin-A-stimulated dog peripheral blood mononuclear leucocytes isolated from a Leishmania–infected dog was reverse transcribed into

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