In situ lymph node imaging

Tracing Antiviral CD8+ T Cell Responses Using In Vivo Imaging

Scientists have long valued the power of in vivo observation to answer fundamental biological questions. Over the last 20 years, the application and evolution of intravital microscopy (IVM) has vastly increased our ability to directly visualize immune responses as they are occurring in vivo after infection or immunization. Many IVM strategies employ a strong multiphoton laser that penetrates deeply into the tissues of living, anesthetized mice, allowing the precise tracking of the movement of cells as they navigate complex tissue environments. In the realm of viral infections, IVM has been applied to better understand many critical phases of effector T cell responses, from activation in the draining lymph node, to the execution of effector functions, and finally to the development of tissue-resident memory. In this review, we discuss seminal studies incorporating IVM that have advanced our understanding of the biology of antiviral CD8⁺ T cells.

General approach to adoptive transfer and cell labeling for immunoimaging

Imaging the single-cell dynamics of the immune system within an intact environment requires the ability to look deep inside tissues and organisms with spatial and temporal resolutions adequate to track cell morphology, motility, and signaling processes, all while minimizing perturbation of the system under study. Fluorescence techniques are highly suited for this purpose, permitting both labeling of specific cells, organelles, or proteins and functional readout of physiological events, and two-photon microscopy allows these processes to be visualized within native tissue environments. Adoptive transfer, as described here, is the generally preferred method for introducing labeled cells of interest into a host animal for immunoimaging. Cells are derived from a donor animal with a genetic background identical to that of the host and can either be endogenously fluorescent (e.g., isolated from a transgenic mouse expressing the fluorescent protein) or can be labeled before transfer. Typically, transferring 2-6 × 106 labeled cells of a given type results in an appropriate cell density for two-photon imaging.

Induction of an immune response for imaging antigen-presenting cell/T-cell interactions

Activated dendritic cells (DCs) are the most efficient antigen-presenting cells (APCs) in the immune system. This protocol describes three different methods to activate antigen-specific CD4+ T cells using (i) bone-marrow-derived DCs, (ii) endogenous dermal DCs that drain to the local lymph node (LN), and (iii) tissue-resident APCs in a delayed-type hypersensitivity (DTH) response.

Immunoimaging: studying immune system dynamics using two-photon microscopy

Cells of the immune system explore a wider territory than any other cells in the body. Responses to a pathogen typically require long-range migration of cells, short-range communication by local chemical signaling, and direct cell-cell contact. Two-photon microscopy allows these processes to be visualized within native tissue environments. Immunoimaging is rapidly developing from a merely descriptive technique into a set of methods and analytical tools that can be used to quantify and to characterize an immune response at the cellular level. This article outlines the hardware required for immunoimaging and discusses methods for quantitative analysis of multidimensional image stacks.