Improved outcome of FAT mice in a model of acute lung injury in spite of increased spleenic lymphocytes apoptosis

ALI and sepsis are still major causes of mortality in intensive care units. After the first hyperinflammatory stage an immunparalyis characterized by apoptosis of spleenic lymphocytes (SL) ensues. Lipid mediators derived from n-6 fatty acids (FA) control inflammation and apoptosis. N-3 FA derived mediators display reduced inflammatory potency. FAT mice are capable of synthesizing n-3 FA from n-6 FA.

We induced ALI in wildtype (WT) and FAT mice using 10µg lipopolysaccharide (LPS) intratracheally (i.t.) and isolated lymphocytes from lung (LL) and spleen 0, 4 and 24h later. Using FACS, we differentiated the lymphocytes into subpopulations (CD3/CD19) and determined apoptosis. Further, we lavaged the lung (BAL) for leukocyte count and measured physical activity of the mice.

FAT had significantly lower numbers of leukocytes in BAL at 24h and activity recovered significantly faster compared to WT.

In WT, numbers of LL stayed even over time, while FAT displayed significantly more LL at 24h. In both groups apoptosis peaked at 4h with FAT being considerably higher. Apoptosis of CD3 and CD19+ cells climaxed at 4h in both groups with a significantly higher apoptosis in WT at this time point.

In both groups, number of SL dropped significantly at 24h with apoptosis peaking at 4h, while FAT displaying higher percentages at all time points. In WT, apoptosis of CD3+ SL was increased at 4h but percentages in FAT remained unchanged. In CD19+ SL apoptosis was constant in WT while it increased in FAT mice at 24h.

In conclusion, we were able to evoke apoptosis of SL by inducing ALI. N-3 vs. n-6 FA display a diverging role in controlling ALI and apoptosis. While in WT CD3+ SL had increased apoptosis, apoptosis in CD19+ SL was higher in FAT. Possibly, differenzial apoptosis of CD3/CD19+ SL impacts resolution of ALI.