Brick nexus 4 after flash bootloader

Hello,

I have tried to back on Kitkat on my nexus 4 but after flashing bootloader, my nexus doesn't boot.

Steps I follow :
1 - fastboot oem unlock ==> OK
2 - fastboot flash bootloader bootloader-mako-makoz30d.img ==> OK ?
3 - fastboot reboot-booloader ==> KO, smartphone doesn't boot

I have a black screen. When phone is plugged on AC and I press Power + Volume down for a while (15sec), a red LED blink.

Console output :
sending 'bootloader' (2203 KB)...
OKAY [ 0.078s]
writing 'bootloader'...
OKAY [ 0.297s]
finished. total time: 0.391s
rebooting into bootloader... OKAY [ 0.000s]
finished. total time: 0.016s

Any solution ?

Thanks in advance.