Ba. Blacklaws et al., INITIAL LENTIVIRUS HOST INTERACTIONS WITHIN LYMPH-NODES - A STUDY OF MAEDI-VISNA VIRUS-INFECTION IN SHEEP, Journal of virology, 69(3), 1995, pp. 1400-1407
Reactive changes occurring within lymph nodes draining the subcutaneou
s site of acute infection with maedi-visna virus (MVV) were studied, a
nd the appearance of infected cells correlated with the immune respons
e. Cells infected with virus were detected in the node by cocultivatio
n from day 4 postinfection (p.i.), with maximum numbers being seen bet
ween days 7 and 14, but even then infected cells were rare, with a max
imum frequency of 23 50% tissue culture infective doses (TCID50) in 10
(6) lymph node cells. At later times, infected cells were still detect
ed, but their numbers fell to 1 to 2 TCID50 per 10(6) cells. Virus-spe
cific CD8(+) cytotoxic T-cell precursors (CTLp) were isolated from inf
ected nodes from day 10 p.i. onwards, and T-cell proliferative respons
es to MW were first detected on day 7 and consistently detected after
day 18. Histological analysis showed a vigorous immune response in the
node. There was a marked blast reaction in the T-cell-rich zones, whi
ch was greatest at the time when the number of virally infected cells
was at its height. At this stage, large numbers of plasma cells were s
een in the medullary cords, indicating that extensive T-cell-dependent
B-cell activation was occurring in the T-cell-rich zones. Germinal ce
nters were prominent shortly after the onset of the T-zone response an
d were still present at 40 days p.i. Phenotype studies of isolated lym
ph node cells failed to detect major changes in the proportion or phen
otype of macrophages, CD1(+) interdigitating cells, and CD4(+) or CD8(
+) T cells despite the fact that CD8(+) lymphoblasts form a major popu
lation leaving the node in efferent lymph. This suggests that there is
a balanced increase in the number of all cell types in response to th
e virus within the node and selective migration of CD8(+) lymphoblasts
containing virus-specific CTLp from the node. Virus-specific immune r
esponses are therefore present within the node when infectious virus i
solation is maximal, but cellular immunity may act to control the leve
l of infection from day 18 onwards.