Residual bacterial proteins within the host during chronic intracellular infections may be immunotoxic to the host. Such immunotoxicity can be concentration dependent. To verify this proposition, four groups of rabbits were used as chronic tuberculin inhalation group I with four subgroups 0.00005, 0.0005, 0.005, and 0.05, tuberculin IU each subgroup received the assigned concentration through four weekly 2 ml inhalation dose. Four days later, rabbits were treated with two oral doses of S. typhi O ( 2 ml of 10 IU) a week apart and two intravenous doses of 0.2 ml of 10 IU a week a part followed by one week leave, then blood was collected. NBT neutrophil phagocytosis increased as the tuberculin concentration increased till 0.05 IU. Group I rabbits showed higher NBT than group II. E. rosset T cell count were higher in group II than in group I. LIF percentages were non-significant at 0.00005, 0.0005 and 0.005 and significant at 0.05 in groups I & II. Typical tuberculin, Jon Mote reaction and anergy were noted in skin DTH with tuberculin as well as S. typhi CFCF. IL-4 and IL-10 concentrations equated IL-1α and IL-12 in saline control group, IL-1α and IL-12 showed overwhelming high concentration that exceeds IL-4 and IL-10 in the groups I,II and III, presenting a case of unbalance between pro-inflammatory and anti-inflammatory cytokines. S. typhi "O" agglutinin titres and IgM S. typhi specific indices decreased as tuberculin concentration increased. Conversely S. typhi specific IgG indices increased as the tuberculin concentration increased. The anti-tuberculin antibody titres ranged from 40-80. All these findings were noted in group I, thus , class switching of IgM to IgG were noted but the means of IgM indices were higher (P=0.05) than the means of IgG indices. This means that there is inhibition of class switching of IgM to IgG. The relation between NBT percent and tuberculin concentration both of group I and II were linear till 0.05. Thus in this model the concentration of 0.05 is immunotoxic in form of immunosuppression and immunostimulant as the other lower concentrations. Therefore the developed chronic tuberculin inhalation lapin model is suitable model for chronic residual bacterial protein immunotoxicity in concentration dependant manner.
Key words: Experimental, Chronic, Tuberculin, Lapin, Immune evaluation
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