Abstract: The immune system is our major defense against viruses, tumors and other ‘foreign invaders’. The issue of humans’ defense against viral infections and the reaction of immune system to these infections are the main problems in practical immunology. To understand the integrated behaviour of the immune system, there is no alternative to Mathematical modeling. This current study seeks to extend the one system of two differential equations originally developed by a system of three differential equations. The system was used to model the behaviour of lymphoid cells in the absence of viruses. The steady states and the stability for this differential model were deduced. The model permitted the existence of two types of stationary states. These are a stable state and an unstable state. It was found from the study that a stable state represents the pre-programmed state of the matured lymphoid cells to attack pathogens which may invade the organism. The unstable state represents immuno-deficiency as a result of one or more cells within the immune system not operating properly or the cells are absent altogether.