Autopsy of the body of 6 month old child, who died of sepsis, revealed the absence of thymus and diminished size and weight of the spleen. Microscopy of the spleen detected the absence of periarterial T dependent zones of the follicles and red pulp depletion; In the lymph nodes there is no paracortical zone that is represented mainly by T lymphocytes. B zones in the peripheral immune organs are developed normally. What pathological process is it?