Investigations on in vitro bone resorbing activity from athymic (nude) and euthymic mouse splenic leukocytes

T-lymphocyte dependence of the production of in vitro bone resorbing activity was examined using athymic (nu/nu) and euthymic (nu/+) mouse splenic leukocytes. Conditioned medium (CM) from unstimulated splenic leukocytes of nu/nu mice had greater in vitro bone resorbing activity compared to CM from nu/ + mice (1.7- as compared to 1.2-fold increase of 45Ca release in mouse calvaria). CM from concanavalin A (Con A)-treated nu/nu and nu/+ leukocytes had 1.8-fold and no increase in 45Ca release, respectively. CM from both nu/nu and nu/ + phytohemagglutinin (PHA)-treated leukocytes had a 1.7-fold increase in 45Ca release. Bone resorbing activity from nu/nu CM was inhibited by interferon-τ (10 & 100 IU/mL) and indomethacin (2 × 10 −6 M). CM (untreated or Con A-treated) from nu/nu leukocytes had higher levels of prostaglandin E (PGE) as compared to CM from nu/+ leukocytes, and indomethacin decreased PGE levels in nu/nu CM. Leukocytes from nu/ + mice had increased mitogenesis when stimulated with PHA (1, 3, & 10 μg/mL) or Con A (1 and 10 μg/mL), whereas leukocytes from nu/nu mice were nonresponsive or had significant inhibition of mitogenesis with PHA and Con A. These data indicate that: (a) Conditioned media from splenic leukocytes of nu/nu mice had significant bone resorbing activity which was greater than conditioned media from nu/ + mice; (b) bone resorbing activity in the conditioned media from nu/nu mice was inhibited by indomethacin and interferon-τ; (c) prostaglandin E was present at higher levels in conditioned media (mitogen-treated or untreated) from nu/nu mice compared to nu/ + mice; and (d) mitogenesis in nu/nu mouse splenic leukocytes was inhibited by T-cell mitogens. These results suggest that differences in bone resorbing activity likely reflect the variations in splenic cell populations of nu/nu and nu/ + mice.