CD40L is required for Tat-induced BBB permeability.

<p>(<b>A</b>) Wild-type C57BL/6 (WT) or CD40L deficient (CD40L KO) mice were injected retro-orbitally with HIV Tat (1 µg/g body weight; n = 6 per group), while control mice were injected with saline. Sodium fluorescein (NaF) analysis revealed that the Tat-induced increase in BBB permeability is dependent on CD40L. The values shown here represent fold increase in the ratio of brain versus plasma concentrations of NaF. (<b>B</b>) Complete blood counts reveal that both WT and CD40L KO animals demonstrate a Tat-induced drop in platelet count by 24 h post-treatment. For panels (A) and (B) statistical significance was determined via one-way ANOVA followed by Bonferroni’s test for multiple comparisons and indicated in the figure as *p<0.05. (<b>C</b>) Verification that CD40L expression is absent in CD40L KO animals. Representative results obtained from reverse transcription-PCR of spleen homogenates using primers specific for CD40L and GAPDH. (<b>D</b>) Recombinant mouse sCD40L (rsCD40L; 0.2 µg/g body weight) was injected intraperitoneally into WT animals (n = 4). Twelve hours post-treatment NaF assays were performed and it was revealed that rsCD40L induced similar BBB permeability as treatment with Tat alone. An unpaired t-test indicated that p = 0.0531. sCD40L ELISA confirmed that there was a significant increase in circulating sCD40L following treatment with rsCD40L (right panel), and an unpaired t-test determined statistical significance as ***p<0.001.