Abstract
The local and systemic immune response to rotavirus was investigated, both
in previously exposed adult sheep and gnotobiotic lambs.
Vaccines were used parenterally to boost the local and systemic humoral
immune response of adult sheep. The response was evaluated by assays for rotavirus
(RV)-specific IgA and IgG antibodies and vims neutralising activity (VNT) in
serum, nasal secretions, and intestinal scrapings. Sheep vaccinated (n=12)
parenterally with a standard rotavirus vaccine (IFA and inactivated rotavirus lysate
(low dose)) showed a significant (p<0.05) increase in RV IgA antibodies in nasal
secretions and intestinal scrapings 2 weeks after vaccination. Sheep vaccinated (n=4)
parenterally with different adjuvants and antigen doses showed both dose-related and
adjuvant-related effects in RV IgG antibodies in serum and nasal secretions 2 weeks
after vaccination. At a low virus dose, ISCOMs and IFA induced a significantly
(p<0.05) higher humoral immune response compared with microspheres, however at
a high dose (inactivated purified virus), ISCOMs and microspheres induced a
significantly (p<0.05) higher humoral immune response compared with IFA. The
immune response after parenteral vaccination is dose- and adjuvant-dependent.
Sheep vaccinated (n=4) orally with live virus, with different adjuvants and
antigen doses showed no significantly increased humoral immune response. No dose
effect or adjuvant effect was observed.
More extensive techniques were used to characterise the primary immune
response in gnotobiotic lambs after infection with a lamb-passaged rotavirus strain
K923. Lambs (n=10) were infected at 6 days of age and killed over a 7 week time
interval together with controls (n=6). RV antibodies and VNT were determined in
serum, nasal secretions, and intestinal scrapings. RV antibody producing cells were
enumerated in blood. Lymphocyte populations in blood and GALT were analysed.
Lymphocyte proliferations were determined in blood and GALT and cytokine
expression was analysed in JPPs and MLNs.
Infected lambs cleared the virus by 8-9 days post-infection without showing
any clinical signs. RV IgA antibody-secreting cells (ASC) in blood and RV IgA
antibodies in serum and nasal secretions were detected from 7 days after infection
v
followed at 10 days after infection by RV IgG ASC and antibodies. RV IgA
antibodies dominated after an infection with rotavirus. RV IgA antibodies were not
detected in intestinal scrapings in the first 10 days after infection, however at 52 days
after infection rotavirus-specific IgA antibodies were observed. Lymphocyte
proliferation was seen in JPPs at 52 days after infection. No significant changes were
observed in lymphocyte sub-populations. IFNy transcripts were expressed in JPPs
and MLNs in both groups and infection had no effect on the expression of IFNy. IL-4
transcripts increased with time but the infected group showed a higher expression at
3 and 52 days after infection. The first evidence of an immune response was seen in
the increased level of IL-4 3 days after infection, which preceded the presence of RV
IgA and IgG antibodies in serum and mucosal surfaces. IL-6 transcripts were
expressed and increased with time in the infected groups. No clear evidence for
CD8+ T cell or rotavirus-specific secretory antibody involvement in viral clearance
was found suggesting that other mechanisms may play a role.
Vaccines composed of either rotavirus mixed with ISCOMs or recombinant
VP6 incorporated into ISCOMs were used to examine if one oral dose could induce a
mucosal immune response and protection against subsequent challenge. Gnotobiotic
lambs were vaccinated orally either with PBS/ISC, inactivated rotavirus (IRV)/ISC,
recombinant VP6/ISC, or IRV alone, challenged 3 weeks later with a live lambpassaged strain, and killed 8-9 days after challenge. The immune response was
measured as described above. The rotavirus-vaccinated groups had RV IgG ASC and
antibodies in blood from 7 and 11 days respectively. After challenge, rotavirusvaccinated groups cleared the virus in a reduced period (7.0 days vs 9.0 days),
however this was only significant (p<0.05) in the IRV/ISC group. RV IgA antibodies
were observed in serum and nasal secretions from 4 days after challenge. In intestinal
scrapings, these were significantly (p<0.05) higher in the IRV/ISC and IRV groups.
RV IgG antibodies were significantly (p<0.05) increased in nasal secretions and
intestinal scrapings in the IRV/ISC and IRV groups. Lymphocytes from JPPs
proliferated significantly against rotavirus in the IRV/ISC and IRV groups. CD45R+
cells were significantly increased in blood in the IRV/ISC group before challenge,
however no differences were found in other lymphocyte sub-populations either in
blood or GALT. A down-regulation of IFNy transcripts was observed in JPPs and
vi
MLNs in the IRV/ISC group while the VP6/ISC group had a higher expression
compared with the PBS/ISC and IRV groups. IL-4 transcripts were low in MLNs in
all groups but in JPPs the rotavirus-vaccinated groups had a higher expression. IL-6
transcripts in JPPs were higher in the IRV/ISC and VP6/ISC groups but in MLNs all
rotavirus-vaccinated groups had a higher level of expression. One oral dose of
inactivated rotavirus alone, mixed with ISCOMs, or recombinant VP6 incorporated
into ISCOMs can induce priming and partial protection. These results suggest also
that different immunological mechanisms take place when different vaccination
protocols are used.
