Large granular lymphocytes (LGL) with a T or natural killer (NK) lymphoblast morphology and indiscriminate (non-major histocompatibility complex-linked) cytotoxicity for a variety of target cells can be derived in culture from the tissues of animals infected with either alcelaphine herpesvirus-1 (AlHV-1) or ovine herpesvirus-2 (OvHV-2). In this study, LGL survival in the absence of exogenous
interleukin-2 was inhibited by the
protein kinase inhibitor genestein, but not the
p70 s6 kinase inhibitor
rapamycin. Constitutive activation of the
src kinases Lck and Fyn was demonstrated in a bovine LGL line infected with OvHV-2 and in two rabbit LGL lines infected with AlHV-1. The p44 erk1 and p42 erk2
mitogen-activated protein kinases (MAPK) were also constitutively activated in the LGLs but not control T cells. Lck and Fyn
kinase activity in the LGLs did not increase after
mitogen (
concanavalin A or
concanavalin A plus
phorbol ester) stimulation of the cells, in contrast to control T cells. Control T cells, but not the LGLs, proliferated after
mitogen stimulation. An analysis of
tyrosine phosphorylated
proteins in the cells indicated that the LGLs exhibited some similarities and differences to activated control T cells. The results demonstrate that the activated phenotype of the LGLs, associated with
malignant catarrhal fever virus infection and in the absence of exogenous
interleukin-2, involves constitutively activated Lck and Fyn
kinases. These are normally crucial for the initial activation of T cells via several
cell-surface receptors (e.g. the
T-cell receptor and CD2). The inability of the LGLs to proliferate in response to
mitogen may be due to an inability of Lck and Fyn to become further activated after
mitogen stimulation.