2.6. Dot ELISA with recombinant hexon protein
Detection of antibodies to FAdV-4 in serum sample by Dot
ELISA was done as described earlier (Roy and Venugopalan, 1999;
Manoharan et al., 2004) with modifications. In short, the recombinant
hexon antigen of FAdV-4 (50 ng/l) was separately spotted at
1 l volume onto nitrocellulose membrane immunocomb strips.
The antigen spotted combs were incubated at 37 ◦C for 1 h in a
humid chamber. After 1 h of incubation the combs were washed
three times with PBST and incubated for 60 min in blocking buffer.
The combs were again washed three times with PBST and then incubated
at 37 ◦C for 45 min with sera samples from the field or sera
sample collected from experimentally vaccinated birds at a dilution
of 1:25, 1:50, 1:100, 1:200 and 1:400 in serum dilution buffer. After
incubating with sera sample the strips were washed three times in
PBST and incubated at 37 ◦C for 30 min with anti-chicken IgY HRPO
conjugate diluted 1:500 in conjugation dilution buffer. After washing,
the combs were exposed to the substrate (5 mg of DAB in 10 ml
of distilled water and 10 l of hydrogen peroxide) for 10 min. The
enzymatic reaction was stopped by washing the combs with tap
water. The positive reaction was indicated by the appearance of a
brown dot.