Effect of time of Porphyridium sp. polysaccharide addition on MuLV progeny release Polysaccharide (100 μg/ml) untreated cells (◆) or treated at the time of infection (■), 24 h (●) or 48 h (◆) postinfection (p.i.), were inoculated with MuSV/MuLV. Two hours after inoculation, unadsorbed virus was removed by three washes, and the cells were covered with fresh medium containing the polysaccharide in all treated cultures. Virus release was followed by assaying viral reverse transcriptase activity in aliquots taken from the culture medium at various times after inoculation. h means hours. Data are mean ± SD, (n = 4).