Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: April 2, 2001
Publication Date: N/A
Technical Abstract: As one of the first steps in the process of immune cell activation, an appropriate stimulus triggers an increase in intracellular Ca2+ ([Ca2+]i) from [Ca2+]i stores. Plasma Ca often decreases in dairy cows at parturition due to the onset of milk production. We hypothesized that hypocalcemia affects [Ca2+]i stores and therefore blunts the release of [Ca2+]i in response to activating stimuli in immune cells. This blunted release of [Ca2+]i leads to reduced immune cell function. Blood samples were obtained from 13 Jersey cows from -2 to 2 wk after parturition, 3 times a week. [Ca2+]i response was measured after stimulation of peripheral blood mononuclear cells by CD3 monoclonal antibody in combination with a secondary antibody, or H2O2 in the presence of extracellular Ca. [Ca2+]i stores were estimated by analysis of [Ca2+]i released after stimulation by pervanadate and ionomycin, which initiate release of [Ca2+]i from mitochondria and endoplasmic reticulum, in the absence of extracellular Ca. [Ca2+]i was measured by ratiometric analysis of Fluo-4/Fura-Red ratios using flow cytometry. Plasma Ca of the cows reached nadir (approx. 6 mg/dl) at calving. [Ca2+]i response to stimuli tended to decrease as calving approached, but significantly increased following calving. This was true, whether CD3 antibody or H2O2 was used to activate the cells. [Ca2+]i stores followed a similar pattern, sugesting that the hypocalcemia commonly observed in periparturient dairy cows may reduce [Ca2+]i stores of immune cells, reducing their ability to respond to activating stimuli.