Riboflavin storage in earthworm chloragocytes/eleocytes in an eco-immunology perspective

Earthworm immune-competent cells, celomocytes, are easily retrieved for ex vivo analyses. Celomocytes consist of amebocytes and species-specific numbers of chloragocyte-derived eleocytes, the latter accumulating free riboflavin in their chloragosome inclusions. Autofluorescent eleocytes are abundant in Eisenia sp., Allolobophora sp., Dendrobaena sp., Dendrodrilus sp., and Octolasion sp., and their numbers and riboflavin contents are affected in species-specific ways by soil quality, as observed by flow cytometry and spectrofluorimetry. The most striking results were obtained in the case of epigeic Dendrodrilus rubidus; in unpolluted soil its riboflavin content was high, but when the earthworm was resident in metalliferous (Pb/Zn- or Ni-polluted) soils, or transferred experimentally from unpolluted to the polluted field soils the riboflavin content was significantly reduced. Such extreme alterations in a cohort of immune-competent cells were not observed in E. andrei, D. veneta, or Al. chlorotica transferred into metalliferous soils. Worms from these three species were also transferred to Zn/Pb/Cd-polluted and unpolluted soils from Southern Poland. It was observed that species-specific changes in riboflavin content occurred not only due to metal pollution, but also other edaphic factors, possibly including organic matter content/quality. Hypothetically, riboflavin status (storage/mobilization) may depend on parasite-immune system balance, which is disrupted by soil-derived stressors, including metals.