Chicken anemia virus (CAV) causes cytopathogenic effects in chicken thymocytes and cultured transformed mononuclear cells via apoptosis. Early after infection of chicken mononuclear cells, the CAV-encoded protein VP3 exhibits a finely granular distribution within the nucleus. At a later stage after infection, VP3 forms aggregates. At this point, the cell becomes apoptotic and the cellular DNA is fragmented and condensed. By immunogold electron microscopy VP3 was shown to be associated with apoptotic structures. In vitro, expression of VP3 induced apoptosis in chicken lymphoblastoid T cells and myeloid cells, which are susceptible to CAV infection, but not in chicken embryo fibroblasts, which are not susceptible to CAV. Expression of a C-terminally truncated VP3 induced much less pronounced apoptosis in the chicken lymphoblastoid T cells. Chicken anemia virus (CAV) transiently causes severe anemia due to destruction of erythroblastoid cells and immunodeficiency due to depletion of cortical thymocytes in young chickens (10, 38). Jeurissen et al. (11) have provided evidence that the observed depletion of the thymocytes occurs via CAV-induced apoptosis. Apoptosis is considered to be a physiological process of cell depletion that is part of the homeostatic regulation of normal tissues (5). CAV in addition to several other viruses, such as human immunodeficiency virus type 1 (2) and parvovirus B19 (19), seems to use apoptosis to exert its cytopathogenic effect. CAV is a small virus with a diameter of about 23 nm and contains a circular single-stranded DNA of 2.3 kb (27). CAV multiplies via a circular double-stranded DNA replicative intermediate, which was recently cloned (18, 21). The cloned CAV genome was proven to be representative for CAV isolates collected worldwide (23, 29). A polycistronic polyadenylated mRNA (22) which comprises three overlapping open reading frames encoding proteins VP1 (51.6 kDa), VP2 (24.0 kDa), and VP3 (13.6 kDa) is transcribed from the CAV

Chicken anaemia virus (CAV) expresses three proteins, VP1, VP2 and VP3, but its capsid contains only the VP1 protein. In this paper, we report that for production of the neutralizing epitope, cosynthesis of (recombinant) VP1 and VP2 has to take place. We show via immunofluorescence that recombinant-baculovirus-infected Sf9 cells synthesizing VP1 (or VP2) alone react very poorly with CAVspecific neutralizing antibodies. In contrast, Sf9 cells co-infected with VP1-and VP2-recombinant baculo-

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