Immune response against P815X2 mastocytoma growing in syngeneic DBA/2 mice. I. Morphometric assessment of lymph node immunoreactivity and analysis of circulating antibodies

To assess the significance of humoral immune mechanisms in host reactivity against the P815X2 mastocytoma grown in syngeneic DBA/2 mice, an approach was made to correlate immunomorphology of the lymph nodes with the functional assays measuring cytotoxic and tumor cell membrane-bound antibodies in mouse sera. Regional and non-regional (RLN, NRLN) lymph nodes, were subjected to stereological analysis to determine the volume fractions (Vv) of the cortex (C), the paracortex (PCA), the germinal centers (GC), and the medulla (M), using a computerized analysis system (IBAS I, Kontron). In both RLN:s and NRLN:s, lymphocyte subsets were identified and their ratios determined using the ABC (avidin-biotin peroxidase complex) technique and following monoclonal antibodies; Anti-Thy 1.2, Anti-Lyt 1, Anti-Lyt 2, and Anti-I-Ad. The 51Cr release assay was used to test the mouse sera for cytotoxic antibodies, and an indirect immunofluorescence (IF) technique to assess the sera for tumor cell membrane-bound antibodies. There was a marked enlargement of the RLN:s reaching the peak on day 12, due to increase of the Vv of the B-zone as well as of the T-zone. Evidence of distinct B-cell stimulation by the growing of P815X2 was provided by an early decrease of Thy1.2+/I-Ad+ cell ratio both in the RLN:s and in NRLN:s. This activation of B-cells seems to be parallel to the elevation of Lyt1+/Lyt2+ ratio in T-cell region on day 6. The IF-tests for or the presence of tumor cell membrane-bound antibodies were almost invariably negative. With exception of two sera, the 51Cr-release assay for cytotoxic antibodies against P815X2 targets was negative. The present study confirms the previous observations on failure to find circulating cytotoxic or cell membrane-bound antibodies in DBA/2 mice bearing P815X2 mastocytoma, despite the morphologically well definable activation in RLN:s and in NRLN:s of the B-cell areas. This is in alignment with the findings in the majority of human tumors, where B-cell predominance in RLN:s does not represent a favourable prognostic sign.