Results
H. polygyrus infection induces blood monocytosis and increases
lung mononuclear phagocytes .
The early response to RSV infection in mice drives the recruitment of
monocytes to the lung causing an accumulation of mononuclear
phagocytes13. In the initial hours of infection these
cells are predominantly Ly6Chi, later downregulating
Ly6C and becoming predominantly CD11c+. Flow
cytometric analysis was used to assess if these populations were also
affected by H. polygyrus infection. Female Balb/c mice were
infected with H. polygyrus and lungs assessed for innate immune
cell composition through the later stages of infection. Cells of the
monocyte-macrophage lineage were identified by their expression of the
high affinity Fc receptor, CD64 (also known as FcγR1), and subdivided on
the basis of SiglecF expression. SiglecF expressing
CD64+ cells represent alveolar macrophages, whereas
the SiglecF– compartment will contain interstitial
macrophages and some monocytes and their progeny. Compared with sham
infection controls there was an increase in the numbers of mononuclear
phagocytes (CD45+, Ly6G-,
SiglecF-, CD11b+,
CD64+, Fig. 1A) in the lungs of H. polygyrusinfected mice from ten days post infection, subsiding yet still elevated
at 14 days. (Fig. 1B). In comparison, the resident alveolar macrophage
compartment (CD45+, Ly6G-,
SiglecF+, CD11b-,
CD64+, Fig. 1A) remained unchanged (Fig. 1C). The
expansion was predominantly due to Ly6C+ macrophages
with a variable increase in CD11c+ only at day ten
(Fig. 1D-F).
A large proportion of the recruited macrophages seen in response to lung
inflammatory stimuli are derived from circulating
monocytes23,24. It is therefore likely that the
vascular monocyte reservoir would reflect the observed influx of
mononuclear phagocytes to the lung. Peripheral blood was sampled from
mice throughout H. polygyrus infection to assess circulatory
monocyte counts by flow cytometry (CD45+,
Lin-, CD11b+,
Ly6G-, CD115+, Fig. 2A). Elevated
total monocyte numbers were observed from seven to ten days post
infection (Fig. 2B) and their numbers returned to baseline by 14 days
post infection. Circulatory monocytes in the mouse can be distinguished
into three phenotypic subtypes; classical, intermediate and
non-classical monocytes25,26. Using the markers Ly6C
and Treml4 to separate these three populations (Fig. 2A), the H.
polygyrus induced expansion of monocytes was found to be predominantly
in Ly6C+Treml4- classical monocytes
(Fig. 2C).