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Glial fibrillary acidic protein (GFAP) is an intermediate-filament (IF) protein that is highly specific for cells of astroglial lineage, although its tissue-specific role is speculative. Determination of the primary structure of this protein should be of importance for understanding the functional role it plays in astroglia. Therefore, we isolated a cDNA clone encoding this protein and determined its nucleotide sequence. The predicted amino acid sequence indicates that GFAP shares structural similarities-particularl in the central rod domain and to a lesser degree in the carboxyl-terminal domain-with other IF proteins found in nonepithelial cell types. Considerable sequence divergence in the amino-terminal region of GFAP suggests that the tissue-specific functions ofthis IF protein might be mediated through this region of the molecule. In contrast, conservation of structural characteristics and a moderate degree of sequence conservation in the carboxyl-terminal region suggest functional similarities. Blot hybridization analysis using the GFAP cDNA as a probe failed to detect GFAP mRNA in both normal and neoplastic human tissues in which IF proteins other than GFAP are known to be expressed.

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Summary Pretreatment of mice with cyclophosphamide (CY) increases susceptibility of adult mice to herpes simplex type I (HSV‐I) infection. In searching for a CY sensitive mechanism, our attention has been focused on natural killer (NK) cells. Activity of these cells was increased in spleens of adult mice after inoculation with HSV‐I and depressed after CY administration. The timing of recovery of NK cell activity after the administration of CY, was consistent with a role for these cells in collaboration with immune T lymphocytes when transferred to pre‐treated, virus infected animals. It is postulated that sensitized T lymphocytes reacting with virus antigens release products that activate macrophages which in turn produce interferon. Interferon increases NK cell activity and NK cells inhibit viral replication. A correlation between resistance to HSV‐I infection and NK cell activity of CBA or C57BL/10 mice was found. It is suggested that NK cells play a role in defence, not only against tumour cells, but also against a wide range of infective agents.

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