Biomedical Engineering Reference
In-Depth Information
Figure 2.5
The contribution to the neutralizing component of fitness of a V3 sequence con-
taining an epitope recognized by an antibody of a given maturity. Fitness is 1 -
N
t
, where
N
t
is
the potency of the antibody at maturity
t
, as determined by the logistic growth equation.
r
is the
intrinsic rate of increase in antibody potency. In this example, the values of the other logistic
parameters are:
K
=
1,
N
0
=
0.001.
its neutralization fitness component, is the product of the fitness effects of each
antibody:
A
W
neut
=
w
α
,
α
=
1
where
A
is the number of antibodies for which the sequence contains epitopes.
2.3.5 Parameter Values
Values for the most important parameters in the model have been determined empiri-
cally. The number of productively infected cells is approximately 10
7
[13]. However,
several recent studies suggest that the effective number of infected cells is much
lower, about 10
3
to 10
4
[14-17]. The effective population size is the theoretical size
that would produce the same amount of genetic drift observed for the real population,
given a constant population size, no selection, and other idealized conditions. This
discrepancy suggests that selection, population subdivision, or other factors result in
a low effective population size. The number of proviruses per infected cell (spleno-
cytes) has recently been observed to be between 3 and 4, with 78 to 80 percent of
infected cells harboring more than one provirus [11]. The number of virions budded
by an infected cell, the burst size, is variously estimated as being about 10
2
to 10
3
,
with the lower number likely more accurate for conditions in vivo [18]. The mutation
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