The 55-6 murine B cell hybri
doma line not constitutively expressing CD40 was treate
d withincreasing amounts of intact anti-mouse surface immunoglobulin G antibo
dy (anti-mIgG) eithernot preincubate
d or preincubate
d for 48 h with lipopolysacchari
de (LPS). In vitro, cross-linkingof surface immunoglobulin G (sIgG) with the whole molecule of anti-IgG antibo
dies in
duce
dthe expression of CD69, CD40, an
d CD19 surface antigens on 55-6 cells. The effect of sIgGligation was
dose-
depen
dent, an
d preincubation with LPS enhance
d their responsiveness to anti-mIgG stimulation. The expression of these surface molecules reache
d the maximum value
during the first part of the cell cycle, correspon
ding to the position of the G1 peak of the DNA
distribution. Stimulation of cells with anti-mIgG
di
d not in
duce changes either in the numberof viable cells or in the fraction of cells un
dergoing proliferation (mitosis). However,preincubation of 55-6 cells with LPS for 48 h before stimulation with anti-mIgG increase
d boththe maximum specific growth rate (
max) an
d the percentage of cells in the G2/M phase, incomparison with non-preincubate
d cells. Moreover, on cells preincubate
d with LPS prior toanti-mIgG treatment, specific IgG2a pro
duction rate was enhance
d significantly compare
d tothat obtaine
d in control cultures. The correlation between the antibo
dy pro
duction rate an
d theamount of IgG that is
detectable on the cell surface was analyze
d by flow cytometry. A goo
dcorrelation between secrete
d an
d surface IgG was observe
d, an
d the results of cell cycle analyses
demostrate
d that the 55-6 hybri
doma cell line has a substantially higher sIgG content in G1phase.