The extracellular aggregation of amyloid b (Ab) peptides and the intracellular hyperphosphorylation of tau at specific epitopes are pathological hallmarks of neurodegenerative diseases such as Alzheimer's disease (AD). Cdk5 phosphorylates tau at AD-specific phospho-epitopes when it associates with p25. p25 is a truncated activator, which is produced from the physiological Cdk5 activator p35 upon exposure to Ab peptides. We show that neuronal infections with Cdk5 inhibitory peptide (CIP) selectively inhibit p25/ Cdk5 activity and suppress the aberrant tau phosphorylation in cortical neurons. Furthermore, Ab 1À42 -induced apoptosis of these cortical neurons was also reduced by coinfection with CIP. Of particular importance is our finding that CIP did not inhibit endogenous or transfected p35/ Cdk5 activity, nor did it inhibit the other cyclin-dependent kinases such as Cdc2, Cdk2, Cdk4 and Cdk6. These results, therefore, provide a strategy to address, and possibly ameliorate, the pathology of neurodegenerative diseases that may be a consequence of aberrant p25 activation of Cdk5, without affecting 'normal' Cdk5 activity.

A type D retrovirus related to but distinct from Mason-Pfizer monkey virus was isolated in vitro from the blood of two rhesus monkeys (Macaca mulatta) with simian acquired immunodeficiency syndrome (SAIDS). Three juvenile rhesus monkeys that were injected intravenously with tissue culture fluids containing this virus developed SAIDS after 2 to 4 weeks.

A virus from fish with lymphocystis disease was isolated in fish cell cultures. Eleven serial transfers were made and the pathognomonic lymphocystis cells were produced in vitro in each transfer. Fish inoculated with 6th- and 9th-passage material developed the disease, and virus was reisolated front them.

Owl monkeys were inoculated intracerebrally, subcutaneously, and intravenously with JC, BK, or SV40 virus. Two of four adult owl monkeys inoculated with JC virus, a human polyomavirus, developed brain tumors at 16 and 25 months after inoculation, respectively. A grade 3 to grade 4 astrocytoma (resembling a human glioblastoma multiforme) was found in the left cerebral hemisphere and brainstem of one monkey. The second monkey developed a malignant tumor in the left cerebral hemisphere containing both glial and neuronal cell types. Impression smears prepared from unfixed tissue of this tumor showed cells that contained polyomavirus T antigen. Virion antigens were not detected. Tumor cells cultured in vitro also contained T antigen but were negative for virion antigen. Infectious virus was not isolated from extracts of this tumor.