Abstract
Summary
Incorporation of specific immune serum in the agar overlay does not inhibit the appearance or normal development of myxoma or fibroma virus plaques. On the contrary, these plaques are clearly visible on an unstained cell sheet; thus enabling an accurate and sensitive plaque count to be made with greater ease at least 2 or 3 days earlier than assays using the standard overlay. The accentuation of the plaques appeared to be due to 2 factors: (1) a precipitate in the agar around the plaque resulting from antibody-antigen reaction, and (2) an increased thickening of the cell layer at focus of infection. The former was directly proportional to the concentration of antibody in the overlay while the latter was related to the percentage of rabbit serum, either normal or immune, in the overlay. A clear distinction between plaques resulting from inoculation of an artificial mixture of myxoma and fibroma viruses was easily provided when fibroma antiserum was present in the overlay since the plaques differed both in size and density. It is suggested that technics reported here might be applicable to other viral assay systems.
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