Page 190 - TBE_Book_V2_2019

Chapter 10: Diagnosis

The test was also used in seroprevalence of titer. The HI test is still used in several
studies because hemagglutinating antibodies countries and is recommended by the World
usually persist for many years. Health Organization for distinguishing
between primary and secondary flavivirus
A further development in the HI test was the infection.
treatment of serum samples with 2-
mercaptoethanol in order to reduce the Immunofluorescence assay
disulfide bonds present in native IgM
15
pentamers to leave inactive IgM monomers. The use of IF to detect antibodies against TBEV
This additional treatment step will cause HI usually involves indirect assays that require
titers to decrease in the presence of IgM cells infected with TBEV to be spotted, fixed,
antibodies, with a significant (at least 4-fold) and permeabilized on slides. A characteristic,
16
decrease in HI titer indicating acute TBEV fluorescent, cytoplasmic staining pattern can
infection. be seen and quantified using serial dilutions of
the serum being tested; antibody isotypes can
One disadvantage of the HI test is that there is be distinguished using fluorescent conjugates
14
a broad cross-reactivity with all flaviviruses specific to IgM or IgG. For IgM testing, the
and therefore samples from patients infected higher-affinity IgG antibodies must be
with more than 1 flavivirus, or from those removed in order to avoid false-negative
recently vaccinated, may lead to non-specific
results. The sensitivity of IF assays appears to
cross-reaction and inaccurate determinations

Figure 2: Schematic diagram of the course of specific anti-TBE antibodies in
primary or secondary flavivirus infection

185
185