AND Logic Gate Error!
I would expect the LED to light dimly with 5V applied to Vb and nothing to Va.

The current will flow through R2 into the base of T2 and then to the LED.

Why do you have the LED and R4 in the emitter of the transistor?

They should be in the collector - the circuit will then work as a AND gate.

It should be similar to below.







simulate this circuit &ndash; Schematic created using CircuitLab