Pharmacokinetics and modeling of immune cell trafficking: quantifying differential influences of target tissues versus lymphocytes in SJL and lipopolysaccharide-treated mice

Abstract

Background: Immune cell trafficking into the CNS and other tissues plays important roles in health and disease. Rapid quantitative methods are not available that could be used to study many of the dynamic aspects of immune cell-tissue interactions.

Methods: We used pharmacokinetics and modeling to quantify and characterize the trafficking of radioactively labeled lymphocytes into brain and peripheral tissues. We used variance from two-way ANOVAs with 2 × 2 experimental designs to model the relative influences of lymphocytes and target tissues in trafficking.

Results: We found that in male CD-1 mice, about 1 in 5,000 intravenously injected lymphocytes entered each gram of brain. Uptake by brain was 2 to 3 times higher in naïve SJL females, but uptake by spleen and clearance from blood was lower, demonstrating a dichotomy in immune cell distribution. Treatment of CD-1 mice with lipopolysaccharide (LPS) increased immune cell uptake into brain but decreased uptake by spleen and axillary nodes.

Conclusions: Differences in brain uptake and in uptake by spleen between SJL and CD-1 mice were primarily determined by lymphocytes, whereas differences in uptake with LPS were primarily determined by lymphocytes for the brain but by the tissues for the spleen and the axillary lymph node. These results show that immune cells normally enter the CNS and that tissues and immune cells interact in ways that can be quantified by pharmacokinetic models.

Figure 1

Uptake over time of ¹³¹I-lymphocytes into brain of CD-1 male and SJL female mice. Upper panel expresses results as %Inj/g of brain tissue and lower panel shows results expressed as brain/RBC ratios. Uptake by SJL mice was 2 to 3 times greater than in CD-1 mice.

Figure 2

Comparison between CD-1 males and SJL females of clearance from blood and uptake by immune tissues of ¹³¹I-lymphocytes. Upper left panel shows clearance of ¹³¹I-lymphocytes from the circulation. The half-time clearance for CD-1 mice was 171 min, but clearance was not measurable for SJL mice. Upper right panel shows that uptake of ¹³¹I-lymphocytes into cervical nodes was high in both SJL and CD-1 mice and did not differ between the strains. Lower left panel showed high uptake of ¹³¹I-lymphocytes by axillary nodes was similar between SJL and CD-1 mice except for the 30 min time point when CD-1 mice had a higher uptake. Lower right panel shows that spleen uptake was the highest of all the tissues examined and that uptake by CD-1 mice was about 2 to 3 times higher than by SJL mice.

Figure 3

Immunohistochemistry and autoradiography of ¹³¹I-lymphocytes. Cervical lymph node lymphocytes from SJL or CD-1 mice were radioactively labeled and injected intravenously into the autologous strain. After 30 min, cervical nodes or brain tissue were harvested, processed, and stained for CD45. Panel A shows ¹³¹I-lymphocyte preparation of cervical lymph node lymphocytes obtained from SJL female mice stained for CD45. Panel B shows stained ¹³¹I-lymphocytes prepared from the cervical lymph nodes of CD-1 males. Panels C and D show CD-1 cervical lymph node cells 30 min after the i.v. injection of ¹³¹I-lymphocytes. Panel E shows stained ¹³¹I-lymphocyte in cortex from SJL mouse. Panel F shows stained ¹³¹I-lymphocyte from hindbrain in SJL mouse. Panels G and H show CD45 stained ¹³¹I-lymphocytes from occipital cortex of CD-1 mice. All magnifications are at 40×.

Figure 4

Comparison among brain regions of uptake of ¹³¹I-lymphocytes in CD-1 mice. The olfactory bulb took up more ¹³¹I-lymphocytes than any other region. No other regions, including whole brain, were statistically different from one another. BR: whole brain; Olf: olfactory bulb; Stria: striatum; Front: frontal cortex; Parie: parietal cortex; Hippo: hippocampus; Hypo: hypothalamus; Thal: thalamus; Occip: occipital cortex; Mid: midbrain; Pons: pons-medulla: Cereb: cerebellum.

Figure 5

Comparison of ¹³¹I-lymphocyte tissue uptake in SJL female and CD-1 male mice. A 2 × 2 design was used where lymphocytes from the cervical lymph nodes of SJL mice were injected into either CD-1 or SJL mice and lymphocytes from the cervical lymph nodes of CD-1 mice were injected into SJL or CD-1 mice. Upper right panel shows that SJL mice tended to have higher levels in the circulation of cells, regardless of source. Consistent with this, Cells (lymphocytes) accounted for only 10% of statistical variance, whereas the Mouse (tissues of uptake) accounted for 46%. Upper right panel shows higher uptake of Cells from either source into brain; statistical analysis showed that Cells accounted for 31% of variance. Lower left panel shows that Cells accounted for 40% of the statistical variance whereas Mouse accounted for 14%. Lower right panel shows uptake by cervical lymph nodes; there were not statistical differences among the four groups.

Figure 6

Uptake of ¹³¹I-lymphocytes in mice treated with LPS. A 2 × 2 design was used, in which cervical-node lymphocytes from LPS-treated or phosphate buffer-treated (PB) mice were harvested, radioactively labeled, and injected i.v. into mice that were treated with LPS or into untreated mice. Upper left hand panel found no difference in levels of ¹³¹I-lymphocytes in the circulation. Upper right panel shows control mice took up more ¹³¹I-lymphocytes than did LPS-treated mice, with Mouse accounting for 42% of the statistical variance; these results show that it was the axillary node rather than the lymphocyte that dominated in determining the degree of uptake. Lower left panel shows similar results for spleen, with Mouse accounting for 72% of the variance. Lower right panel shows that LPS cells were taken up to a higher degree by brain. Statistical analysis showed that Cells accounted for 51% of variance, whereas Mouse accounted for 18% and interaction accounted for 12%.