Calcium signals in single T cells on activation by lectin

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Abstract
Succinylation of concanavalin A (Con A) reduces its oligomer size while retaining its mitogenicity, and provides a probe of T cell activation. We have observed responses of cytosolic ionized calcium to succinyl Con A in suspensions of Jurkat and rat lymph node (LN) cells, using a fluorimeter, and in single cells settled on glass, using a dual wavelength video imaging system. In the fluorimeter a mitogenic level of succinyl Con A (30 μg/ml) produced only a 15–30 nM rise in average cell calcium in the suspended Jurkat or rat cells whereas the use of quantitative video imaging produced asynchronous 250–1000 nM pulses of free calcium in 35% of Jurkat cells and 300–850 nM pulses in 45% of rat LN cells. In Jurkat cells these pulses were sometimes repetitive, giving rise to apparent oscillations. In the fluorimeter 30 μg/ml of native Con A (a supra-mitogenic concentration) produced a 300 nM rise in average cell calcium in suspended Jurkat cells, and a 100 nM rise in rat LN cells; when major histocompatibility complex class II-bearing cells were removed the response rose. Mitogenic Con A (3 μg/ml) produced a much lower rise in calcium. With video imaging the response seen was greater. Levels > 30 μg/ml Con A caused 700–5000 nM pulses synchronously in 94% of Jurkat cells and 250–1000 nM pulses in 73% of rat LN cells. At 3 μg/ml Con A produced asynchronous 300–1100 nM pulses in 36% of rat LN cells. We conclude that the absence of a calcium signal in the fluorimeter can conceal asynchronous calcium responses in individual cells and that brief asynchronous cytosolic calcium pulses are sufficient for lectin to activate rat T cells.