Peripheral blood leukocytes were prepared from 20 ml of heparinized venous blood from healthy adult donors. Polymorphonuclear leukocytes and monocytes, i.e., the potentially phagocytosing cells (nonlymphocytes), are hereafter referred to as PMNms. The method used was adapted from that of Lehmann et al. (23), except cells were washed in RPMI medium (1640 HEPES modification; Sigma R5886) instead of PBS. Briefly, heparinized blood was diluted 1:10 in lysis buffer (0.15 M ammonium chloride, 0.1 M sodium bicarbonate, 0.002 M EDTA · 2H2O [pH 6.8]), left at RT for exactly 10 min, and then centrifuged at 350 × g for 5 min. The supernatant was discarded, and the pellet of cells was washed with RPMI medium (1640 HEPES modification) and centrifuged as before. The lysis step was repeated for 2 to 5 min if a layer of intact erythrocytes was still present. Cells were washed again in RPMI medium, centrifuged, and suspended in 10 ml of PBS. A differential cell count for total numbers of nonlymphocytes and lymphocytes was determined using the Coulter counter, and the percentage of granulocytes was calculated using flow cytometry. The dilution factor was calculated to give a concentration of 1.25 × 107 PMNms per ml. The PMNms were suspended in final buffer immediately before addition to the assay.

Post hoc ergo propter hoc! (latin - correlation does not imply causation).

Just because there is a correlation doesn't mean that the two are linked.  If you did a B cell ELISpot and look for antigen specific B cells you may find that correlates too, this presumable is more likely to be related.  Of course there may be some relationship, perhaps the monocytes are helping to produce the appropriate cytokine milieu which supports plasma cell antibody production but .......