A quantitative measure you could use would be plasma/serum levels of ALT and/or AST. Release of these enzymes occurs during acute inflammation in the liver because of hepatocyte cell death, so it's an indirect measure of an active immune response in the liver. This wouldn't tell you anything about the nature of the immune response though. You can also digest liver and enrich your cell prep for lymphocytes or myeloid cells using a Percoll gradient - you could then perform flow cytometry to look for different cell populations (such as effector T cells) or isolate RNA and look for changes in inflammatory gene expression, etc.

For example:

"Liver lymphocytes were isolated from the liver after perfusion and digestion. Briefly, mice were perfused via the inferior vena cava using digestion media (RPMI-1640 containing 5% FBS; 0.2 mg/ml crude collagenase, Crescent Chemical; and 0.02 mg/ml DNase I, Roche Diagnostics). Livers were forced through a 70-μM filter using a syringe plunger, and debris was removed by centrifugation (30 g for 3 minutes). Supernatants were collected and centrifuged for 10 minutes at 650 g. Lymphocytes were isolated using a 60:40 Percoll gradient"

J. Publicover et. al., Age-dependent hepatic lymphoid organization directs successful immunity to hepatitis B. J Clin Invest. 2013 Sep;123(9):3728-39

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3754256/