Histology of selected immunological organs in polar bear (Ursus maritimus) from East Greenland in relation to concentrations of organohalogen contaminants

Samples of lymph nodes (axillary, n=54 and inguinal, n=45), spleen (n=60), thymus (n=11) and thyroid tissue (n=5) from a total of 82 polar bears (Ursus maritimus) collected in East Greenland 1999-2002 were examined histologically. The purpose was to relate histology to concentrations of organohalogen contaminants (OHCs) [i.e., sum (Σ)PCBs, ΣDDTs, ΣHCHs, ΣCHLs, HCB, Dieldrin and ΣPBDEs] determined in adipose tissue, as studies on polar bears have indicated that some OHCs act as immunosuppressive agents. Secondary follicle counts were evaluated in spleen and lymph nodes, and semiquantitively divided into four groups (0: few/absent to 3: high). In the spleen, a high secondary follicle count was found in 21% of the cases (12/60), and this was significantly higher in subadults (p<0.01) compared to adults of both sexes. Also in the lymph nodes a high secondary follicle count was found in 20% of the cases (20/99), and in the axillary lymph nodes changes were significantly higher in subadults (p<0.05) compared to adults of both sexes. Significantly weak correlations between concentrations of OHCs and the amount of secondary follicles in lymph nodes was found, but probably occurred as a consequence of other multiple stress factor(s) (all: p<0.05) and also one significant, but modest positive correlation was found between ΣPBDE concentrations and secondary follicle counts (p<0.01; r=0.41). In spleen, a significant relation between low concentrations of OHCs in adipose tissue and few/absent secondary follicles was found with respect to ΣCHLs, ΣHCHs, HCB and Dieldrin. No histopathological observations (e.g., neoplasia) were found in spleen or lymph nodes, nor in thymus or thyroid. In conclusion, the present data suggest that the exposure concentrations of OHCs to polar bears are unlikely to have resulted in adverse effects on the tissues in question, although ΣCHLs, ΣHCHs, HCB and Dieldrin were related to increased secondary follicle counts in the spleen.