The critical role of lymph nodes in corneal alloimmunization and graft rejection

To elucidate the role of draining cervical lymph nodes (CLNs) in corneal alloimmunity.

Fully mismatched orthotopic corneal transplantation was performed in BALB/c hosts that had their CLNs excised before transplantation (CLN(-)). Normal hosts (CLN(+)), splenectomized mice (Sp(-)), and those without either CLNs or spleen (CLN(-)/Sp(-)) served as comparison groups. To determine the contribution of CLNs to alloimmunity more directly, CLN(-) mice were reconstituted by grafting LNs from other BALB/c mice to their cervical lymphatic chains, thus deriving CLN(-/+) mice. Tetramethyl rhodamine isothiocyanate's (TRITC) flow to draining CLNs was used as a measure of afferent lymph flow. Graft survival and allospecific delayed-type hypersensitivity (DTH) were used as measures of alloreactivity.

Fifty percent of normal control and 12% of Sp(-) hosts accepted the allografts. In contrast, 100% of CLN(-) and 88% of CLN(-)/Sp(-) hosts accepted allografts indefinitely (P < 0.01). Additionally, all CLN(-) hosts failed to demonstrate allospecific DTH (P < 0.001). CLN(-/+) mice reconstituted with LN from naïve animals showed graft survival rates and DTH responses that were indistinguishable from those of naïve CLN(+) mice. Of particular interest, however, is that mice reconstituted with CLNs from hosts with rejected corneal grafts had swift rejection of subsequent corneal grafts and exhibited strong donor-specific DTH. In contrast, mice reconstituted with CLNs from hosts with accepted corneal grafts showed rejection of subsequent corneal grafts in a manner that was indistinguishable from rejection in naïve CLN(+) hosts.

Draining CLNs play a critical role in allosensitization and rejection. In contrast to the spleen, draining CLNs do not appear to play a critical role in tolerance induction in corneal transplantation.