Influence of applied immunostimulation on the immune response in <i>Steatoda grossa</i> (Theridiidae) spiders under chronic exposure to copper

The objective of this study was to determine whether, and to what extent, long-term oral exposure to copper at sublethal concentrations alters selected parameters of the cellular and humoral immune responses in the spider Steatoda grossa (Theridiidae). Female specimens of S. grossa were subjected to both natural immunostimulation - via bacterial cell suspensions of Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria - and artificial stimulation using phorbol 12-myristate 13-acetate (PMA). This was done to assess quantitative and qualitative changes in haemocyte subpopulations and the concentrations of selected haemolymph proteins between nonstimulated individuals and those that underwent immunostimulation. The percentages of small agranular and granular haemocytes remained consistent across all experimental groups, regardless of the immunostimulant applied, in both the control and copper-intoxicated spiders. However, the percentage of large agranular cells was significantly higher in spiders that received copper in their diet compared to the control group. Furthermore, copper exposure at the tested sublethal concentration and duration led to an increased frequency of necrosis within the granulocyte subpopulation. Among spiders fed prey supplemented with copper, a statistically significant increase in cecropin-like peptide levels was observed only following exposure to the G- bacterial suspension. In contrast, an increase in defensin-like peptides was recorded after PMA-induced stimulation. In the control group, all types of immunostimulation resulted in increased levels of metallothionein-like protein (MTs), although these differences were not statistically significant. A similar upward trend in MT protein levels was noted in copper-exposed individuals, with the highest levels observed in spiders additionally treated with the G- bacterial suspension. These results suggest that dietary copper modulates the immune response in S. grossa, with the effects varying depending on the type of immunostimulant applied.