Transforming growth factor-beta induced by live or ultraviolet-inactivated equid herpes virus type-1 mediates immunosuppression in the horse.

Up to 21 days after exposure to live or ultraviolet-inactivated equid herpesvirus type-1 (EHV-1) autologous serum from ponies caused an immunosuppressive effect if incorporated into T-cell proliferation assays to EHV-1. The suppressive factor in the sera of ponies also inhibited T-cell response to phytohaemagglutinin. Increased levels of circulating activated transforming growth factor-beta 1 (TGF-beta 1) were detected, and the suppressive activity of the serum could be reversed by antibody to TGF-beta 1. In a challenge experiment the ponies which exhibited circulating TGF-beta 1 activity succumbed to infection while the ones with similar magnitudes of T-cell responses, but no TGF-beta 1 activity, were protected. A definition of this immunosuppressive mechanism and its mode of induction must be central to the design of vaccines and to an understanding of the pathogenesis of EHV-1.

Immunogenicity of equine herpesvirus type 1 (EHV1) and equine rhinovirus type 1 (ERhV1) following inactivation by betapropiolactone (BPL) and ultraviolet (UV) light.

Some kinetic data on the inactivation of equine herpesvirus type 1 (EHV1) and equine rhinovirus type 1 (ERhV1) by betapropiolactone (BPL) and ultraviolet (UV) irradiation are reported. 0.25% BPL at 37 degrees C for 1 h reduced the titre of EHV1 by greater than 10(3 . 4) and of ERhV1 by greater than 10(4 . 1) TCID50/ml. UV irradiation (334 microW/cm2) produced similar reductions in titre after 2 min. These data were used as a basis for inactivating EHV1 and ERhV1 by the combined action of BPL and UV irradiation. Viruses were exposed to 0.1% BPL for 1 h at 4 degrees C with constant stirring, followed by UV irradiation for 2 min, followed by incubation for 3 h at 37 degrees C. Inactivated EHV1 elicited secondary immune responses only in horses whereas ERhV1 produced primary immune responses in mice (including athymic nu/nu mice), rabbits and probably in horses.

Biochemical transformation of deoxythymidine kinase-deficient mouse cells with UV-irradiated equine herpesvirus type 1.

A line of 3T3 mouse cells lacking deoxythymidine kinase (dTK-) was stably transformed to the dTK+ phenotype after exposure to UV-irradiated equine herpesvirus type 1 (EHV-1). Biochemical transformants were isolated in a system selective for the dTK+ phenotype (Eagle minimal essential medium containing 10(-4) M hypoxanthine, 6 X 10(-7) M aminopterin, and 2 X 10(-5) M deoxythymidine). Transformation was accompanied by the acquisition of a dTK activity with immunological, electrophoretic, and biochemical characteristics identical to those of the dTK induced by EHV-1 during productive infection. The transformed cells have been maintained in selective culture medium for more than 50 passages and have retained the capacity to express EHV-1--specific antigens. Spontaneous release of infectious virus has not been detected in the transformed lines, and the the cells were not oncogenic for athymic nude mice. In contrast to normal dTk+ 3T3 cells, EHV-1 transformants were unable to grow in the presence of arabinosylthymine, a drug selectively phosphorylated by herpesvirus-coded dTK's. These results indicate that a portion of the EHV-1 genome is able to persist in the transformed cells for many generations and be expressed as an enzymatically active viral gene product.