Spatiotemporal Three-Dimensional Quantitative Visualization of Macrophage Phagocytosis of Adjuvants In Vivo Using Optical-Resolution Photoacoustic Microscopy

As
a crucial component of vaccines, adjuvants rely on the ability
of macrophages to phagocytose for immune activation. It is extremely
valuable to capture this complex process accurately. In this study,
we constructed an optical-resolution photoacoustic microscopy (OR-PAM)
system with lateral and axial resolutions of 630 nm and 2.52 μm,
respectively, enabling high-resolution three-dimensional visualization
and quantitative analysis of the adjuvant phagocytosis process of
macrophages. OR-PAM results showed that compared with undifferentiated
monocyte macrophages (M0), classically activated macrophages (M1)
had profound phagocytic ability to label CpG oligodeoxynucleotides
with gold nanoparticles (AuNPs) (CpG–Au) and aluminum adjuvant
labeled with lumogallion (Alum–Ga), consistent with the phagocytic
observations of AuNPs. In addition, the TNF-α, IL-6, and IL-1β
released by M1 were significantly higher than those released by M0
within 2 h after CpG–Au and Alum–Ga stimulation. These
results indicated that the size of the adjuvant can affect the phagocytosis
efficiency of the macrophages. The findings provide a better understanding
of the adjuvant-induced macrophage response and help to develop more
efficient and specific vaccines.