TABLE 4.

EBV-infected naive B cells from tonsils are CD80 positive^a

Expt	No. of infected cells/107 B cells
	IgD+	IgD+ CD80−	IgD+ CD80+
1	75	4b	400
2	420	170	5,600

^aFrequencies are expressed as the absolute number of virus-infected cells per 10⁷ B cells in the population. The frequencies were measured as detailed previously (12). Briefly, purified cell populations were serially diluted, and multiple aliquots were made of each diluted sample. DNA PCR was then performed on each aliquot, the fraction of negative aliquots for each dilution was estimated, and Poisson statistics were used to calculate the frequencies. Since the DNA PCR will detect a single genome of viral DNA, this assay provides an absolute quantitative measure of the frequency of infected cells. There were 31% and 10% CD80⁺ cells in the IgD⁺ fraction for experiments 1 and 2, respectively. 

^bBased on a single positive cell among 2.2 × 10⁶ cells tested.