Liver sinusoidal blood containing natural killer-like cells

Liver sinusoidal lymphocytes: their immune functions

Recent studies strongly suggest that the liver plays an important immunoregulatory role. Evidence of its role in general immune responsiveness originates from observation that, in recipients of liver grafts, the survival of other allografts is significantly prolonged. The question arises as to which blood lymphocyte subsets, most likely to be responsible for this phenomenon, marginate in liver sinusoids. To study this problem, a liver ex vivo perfusion model was designed for rats. In situ W/WAG livers were washed clear of sinusoidal marginating cells prior to and after 1 h perfusion with syngeneic blood. The number of blood cells retained in liver sinusoids, their phenotypes, the responsiveness to mitogen (PHA, 90 micrograms/ ml) and cytotoxicity against YAC-1 tumour cells were examined. Our studies showed that rat liver retains in the sinusoids a population of blood cells, enriched in NK, CD8+ and MHC class II+ cells, displaying a high cytotoxic activity and low responsiveness to mitogen stimulation, with a capacity of about 10(6) cells/g of tissue.

Functional characterization of liver-associated lymphocytes in patients with liver metastasis

BACKGROUND

The liver-associated lymphocytes (LAL) population is mainly composed of cells with natural killer (NK) activity expressing the CD3+/-CD56+ phenotype. No evident difference has been found in the phenotypic data between patients with benign or malignant liver disease. In this study, the cytotoxic pattern of this population has been characterized from patients who underwent an operation for benign or metastatic liver disease.

METHODS

LAL were isolated by sinusoidal high-pressure lavage from partial hepatectomies. Phenotype was characterized by flow cytometry, and cytotoxicity was evaluated by standard 4-hour 51Cr release assays against NK and lymphokine-activated killer (LAK)-sensitive targets.

RESULTS

In patients with benign liver disease, LAL showed spontaneous high levels of NK activity and LAK activity compared with peripheral blood lymphocytes. In patients with metastatic liver disease, no difference was observed in the levels of NK activity between LAL and peripheral blood, and the level of LAK activity was far lower than that expressed in patients with benign liver disease.

CONCLUSIONS

These results show that the cytotoxic pattern of peripheral blood lymphocytes does not mirror that of LAL. In patients with benign liver disease, LAL are in a state of activation, whereas the decreased level of LAL cytotoxicity in patients with metastatic liver disease suggests that the cytotoxic activity of these cells could be inhibited by the presence of suppressive factors.

Influence of whole-body hyperthermia on natural cytotoxicity of liver blood-borne sinusoidal cells

Rat liver sinusoidal cytotoxic cells were examined after exposure to in vivo and in vitro hyperthermia at 40-41 degrees C. Whole-body hyperthermia lasting for 4 h caused a decrease in the cytotoxic activity of liver sinusoidal washout cells against YAC-1 and K562 cells. Surprisingly, the percentage of washout cells with morphology of LGL (large granular lymphocyte) increased both in the liver washout and in portal blood compared to control normothermic animals. The proportions of phenotypically characterized cell subpopulations isolated from liver sinusoids did not change. Elimination of i.v. injected 125I-labelled K562 cells was decreased during hyperthermia. In vitro incubation of liver sinusoidal cytotoxic cells for 3 h at 41 degrees C decreased their cytotoxic activity by affecting the process of effector-target cell binding. However, once the effector-target cell conjugates were formed, the cytotoxic process proceeded as in normothermic conditions. These data suggest that inhibition of liver sinusoidal cytotoxic cell activity after hyperthermia may be a result of deficient target cell recognition by the effector cell.

Liver sinusoidal cytotoxic cells are recruited from blood and divide locally

Liver sinusoids contain marginated mononuclear cells which are highly cytotoxic against several tumor cell lines. These cells may play an important role in the elimination of tumor and viral antigens of enteric origin. The question arises whether they are bloodborne, temporarily resident, replacable or permanently resident cells. In order to obtain the answer, a cytogenetic analysis of sex chromosomes in the mononuclear cells from a liver sinusoidal washout of male Lewis rats who had received liver transplants from syngeneic female donors was performed 4 weeks after grafting. About 9% of the liver sinusoidal mononuclear cells obtained from both control and transplanted livers showed mitotic activity, whereas no dividing cells could be found in peripheral blood. In all experiments karyotypic studies of these dividing liver sinusoidal mononuclears from female livers transplanted to syngeneic males revealed in all experiments the male (XY) karyotype. This finding indicates that the cells under study were of blood origin and are not a constitutive cellular component of the liver. They are probably recruited by the liver and divide locally at a signal of a so far unknown origin.

Characterization of liver-associated natural killer cells in patients with liver tumors

The existence of a marginal lymphocyte population in rat liver sinusoids has already been demonstrated using the sinusoidal lavage method. We used the same technique to study the lymphocyte population in human liver obtained ex vivo after partial hepatectomy for benign or malignant tumors and compared it with peripheral and portal blood lymphocyte populations. Percentages of lymphocyte surface phenotypes were evaluated by flow cytometry. The lymphocyte population obtained from human liver is mainly made up of CD56+ (35%) cells. This percentage is three times greater than that found in peripheral and portal blood. Two-color flow cytometry analysis showed that within the CD56+ liver cell population, at least three distinct subsets could be found: (a) CD3+/CD56+/CD16-; (b) CD3-/CD56+/CD16-; and (c) CD3-/CD56+/CD16+. Although these subsets were also present in peripheral and portal blood, the percentage distribution was completely different because most CD56+ cells in peripheral and portal blood belonged to the CD3-/CD56+/CD16+ subset. These results show the existence of a heterogeneous natural killer cell population in human livers with tumors. The functional significance of this heterogeneity still needs to be explained.