Mechanism of graft-versus-host-induced lymphadenopathy in mice. Trapping vs. proliferation

Polyhalogenated dibenzo-p-dioxins and dibenzofurans and the immune system. 3. No immunosuppressive effect of 2,3,7,8-TCDD in the popliteal lymph node assay (PLNA) in rats

We used a modified version of the popliteal lymph node assay in rats to investigate the immunosuppressive potential of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In 10 months we conducted 3 experimental series. Animals were treated with single s.c. injections of TCDD and 7 days later human red blood cells (HRBC) were injected s.c. into the right hind footpad of the rat. Another 7 days later, both popliteal lymph nodes were prepared, weighed, the cell number was counted and the quotients ("index") of these variables from the treated and the untreated side were determined. The doses applied in three experimental series were 600', 60, 6, 0.6, and 0.06 ng TCDD/kg body wt. In the first experimental series only the three highest doses were tested, in a second experimental series doses of 60, 6, 0.6, 0.006 ng TCDD/kg body wt were applied. Combining the results of these two experimental series, a statistically significant difference was found in the cell number index between the controls and the two highest doses tested (60 and 600 ng/kg body wt; p less than 0.01). This result was recently published as an abstract (Korte et al. 1990). However, with slight methodological changes in the third series of experiments (doses applied: 600, 60, 6, 0.6, and 0.06 ng TCDD/kg body wt) and using a greater number of animals we could not confirm these preliminary results. No difference was seen in the immune response to the antigen challenge in controls and in any of the treatment groups. We conclude that TCDD does not clearly influence the immune response as observed in the popliteal lymph node assay under our experimental conditions.

Murine cortical brain cells are autoantigenic from a distinct developmental stage onwards

The expression of autoantigens on murine cortical brain cells and their first appearance during development was studied. Autoreactivity was analyzed by weight increase and lymphocyte proliferation in the popliteal lymph node (PLN). Cortical brain cells or defined plasma membrane preparations were injected s.c. without adjuvant into syngeneic recipients. Weak, but significant T cell-dependent PLN enlargement was triggered with brain cells from adult mice. A stronger reaction could be elicited with one defined fraction of purified plasma membranes. The earliest appearance of the antigenic material in the plasma membrane fraction was observed on day 15 after birth. This time point correlates exactly with the completion of the blood-brain barrier in large parts of the central nervous system.

Graft-vs.-host reactions: mechanisms and contemporary theories

A graft-vs.-host (GvH) reaction can be initiated by injection of immunocompetent lymphocytes into a histoincompatible host that is unable to reject these cells. The reaction is characterized by splenomegaly, hepatomegaly, lymph node atrophy, body weight loss, dermatitis, and diarrhea, often leading to mortality. The onset and severity of the GvH reaction are determined by differences in histocompatibility antigens between the donor and the acceptor, and by the number and nature of the transplanted allogeneic cells. Many different in vivo and in vitro systems have been devised for experimental studies of the GvH reaction. In several of these models, however, different parameters are measured. Furthermore, the conclusions drawn from these investigations sometimes contradict each other. This paper reviews the experimental data, and discusses the mechanisms underlying the GvH reaction.

Cyclosporin-A inhibits accumulation of lymphocytes within lymph nodes

The ability of cyclosporin-A (CS-A) to modify lymphocyte accumulation, seen in lymph nodes draining a site of antigen deposition, has been compared with the effect of other drugs known to affect lymphocytes and/or macrophages. CS-A markedly inhibited lymphocyte accumulation in a dose-related manner, whereas aspirin, BW755c (3 amino 1 [m (trifluoromethyl) phenyl] 2-pyrazoline) and hydrocortisone were without effect. Indomethacin produced inconclusive results. The time of CS-A administration was critical, the drug needing to be present before antigen inoculation, being ineffective if given 23 hr after antigen.

The sequence of changes in blood flow and lymphocyte influx to stimulated rat lymph nodes

The rat popliteal lymph node was studied from 1 hr to 8 days after the footpad injection of either sheep erythrocytes or syngeneic rat erythrocytes. The following were measured relative to the contralateral (unstimulated) lymph node: (i) blood flow; (ii) lymph node weight; (iii) influx of lymphocytes from the blood; (iv) [3H]-thymidine incorporation; (v) [35S]-sulphate incorporation into macromolecular form (chiefly by high endothelial venules). After the arrival of sheep erythrocytes all five quantities showed substantial increases which began in a definite sequence. The blood flow started to rise first and may have been the main factor contributing to the later increase in lymphocyte influx. Increased sulphate incorporation began later than the rise in lymphocyte influx. After the injection of rat erythrocytes a small increase in lymphocyte influx was found without a corresponding increase in blood flow. In rats irradiated before the footpad injections lymphocyte influx increased three-fold after sheep erythrocytes, rat erythrocytes or PBS, again without a corresponding increase in blood flow. Thus while variation in blood flow to high endothelial venules is one important factor in determining the supply of lymphocytes to the lymph node other factors are operative in certain situations.

The host component of the popliteal lymph node graft-versus-host (GVH) reaction. Identification of cells in the node and kinetics of cell proliferation

The cellular composition of rat popliteal lymph nodes undergoing a GVH reaction was examined. The great majority of cells isolated from the nodes were lymphocytes, while the contribution of phagocytic cells was negligible (less than 5%). Both T and B cells were present in GVH nodes. However, the proportion of B cells was higher than in normal lymph nodes (40-50% vs 30%). Cells synthesizing DNA were enumerated autoradiographically in sections of GVH nodes up to day 7 of the response. A significant increase in the proportion of 3H thymidine labelled cells had already been found on the third day of the GVH response, before lymph node enlargement was apparent. Of the differnt days tested a maximum of 6% labelled cells was found on day 7. Liquid scintillation counting of cell suspension from such nodes showed an even higher increase in 3H thymidine incorporation in GVH vs normal nodes. These findings indicate that cell proliferation is a central mechanism behind the lymph node enlargement.