PCOS appeared to have an enhancing effect on the levels of P. gingivalis and F. nucleatum and their association with gingival inflammation, hinting towards a microbial specificity. Measurement of serum antibody levels provides information on host reaction to the oral microbiota, as they may be associated with the progression from periodontal health to disease, or define disease-susceptible or disease-resistant individuals. In systemically healthy individuals there were no major differences in serum antibody levels according to periodontal status, despite differences in the subgingival microbiota However the systemic health Obacunone status may alter the serum antibody responses to periodontal pathogens, as demonstrated in patients with poor glycaemic control. To this extent, serum antibody levels to C. rectus were elevated in type 2 diabetes, whereas antibody levels to P. gingivalis were elevated in periodontitis, irrespective of diabetic health status. Recent evidence also shows that serum antibody levels of A. actinomycetemcomitans, P. gingivalis and P. intermedia are associated with an increased risk of coronary heart disease. In the present study, serum antibody levels to P. gingivalis, P. intermedia and S. oralis were elevated in the presence of PCOS. This may indicate that this endocrine disorder may affect the antigenic susceptibility to these species. Although in systemic health no positive correlation was found between gingival Desacetyl-asperulosidic-acid inflammation and serum antibody levels to any of the studied species, in the presence of PCOS a positive correlation was found only for P. gingivalis. Moreover, salivary counts and serum antibody levels of P. gingivalis, as well as F. nucleatum, strongly correlated with each other. Serum antibody levels may provide insights for understanding individual systemic host responses to periodontal microbiota, although the particular associations are not well understood to date. To this extent, a national US survey has shown that demographic, behavioural, oral and general health-related characteristics were strong determinants of systemic antibody responses to periodontal bacteria.