Figure 4.

Polarized expression of p-Lck and p-ZAP-70 in CD8⁺ T cells tightly apposed to astrocytes during clearance of virally infected cells from the brain. Animals were infected unilaterally in the striatum with an adenovirus, and 30 d later they were immunized against adenovirus systemically. The systemic immunization induces a selective infiltration of CD8⁺ T cells into the injected, but not contralateral, hemisphere, which eventually clears infected astrocytes and viral genomes. All images shown represent 0.5-μm-thick confocal optical sections. Panels in A illustrate an activated lymphocyte in close anatomical apposition of the process of an astrocyte. Activation was established by p-Lck (green) immunoreactivity (a) within CD8⁺ (red) lymphocytes (b). Only CD8⁺ T cells that contacted astrocytes directly (GFAP⁺ processes) were immunoreactive for p-Lck, indicating the selective activation of T cells (a and b). White arrows indicate that the CD8⁺ T cell is contacting a GFAP-immunoreactive process (magenta) (c and merged images). DAPI nuclear staining (blue) was used as a cellular counterstain. Minimal T cells were observed within the noninjected hemisphere (not depicted). P-Lck within the CD8⁺ T cells was polarized to the T cell's membrane in close contact with the astrocyte's process (white arrow in merged images). B represents a three-dimensional reconstruction of the contact illustrated in A; the confocal image of the contact area is shown in a; b illustrates the color scales for A and B, including colors of areas of overlap between fluorophores. C illustrates the polarized expression of phosphorylated ZAP-70 in several CD8⁺ T cells during the clearance of infected GFAP⁺ astrocytes from the brain; p-ZAP-70 (green), CD8 (red), GFAP (magenta or white), and DAPI (nuclear marker in blue). Note that ZAP-70 is polarized to the site of contact between the CD8⁺ T cell and the astrocytes' processes. Bars, 15 μm.