Biomedical Engineering Reference
In-Depth Information
V
()
N
>>
ln
cM
,
[6]
v
0
which shows that
N
, the repertoire size, should scale ~ln(
cM
). Thus, this theory
suggests that there should be only a weak dependence of repertoire size on a
mammal's size.
2.4. Scaling and the Anatomical Features of the Immune System
The lymphocytes of the mammalian immune system not only circulate
throughout the body but also accumulate in the spleen and lymph nodes. These
tissues act as filters, with the spleen trapping antigens from the blood and lymph
nodes trapping antigens that enter the tissues. Because antigens are there, lym-
phocytes search for and interact with antigens in the "secondary lymphoid tis-
sues." An interesting question then is how should the size or mass of the spleen
and lymph nodes scale with body size? Each lymph node "drains" a certain vol-
ume of tissue. Thus, as animals get larger, do lymph nodes simply get larger or
are they more numerous? An appropriate scaling theory of the immune system
should be able to answer these questions. Here, as a first step, we look to see
what data are available and if there is any indication of scaling that is more
complex than that of scaling simply by mass, i.e., ~
M
.
Figure 1
. Number of lymph nodes per individual as a function of body mass for dog, human,
horse, and cow (in order of mass).
