Immunologic memory is established in nursling rats immunized with tetanus toxoid, but is not affected by concurrent...

Experiments were conducted to determine whether nursling rats immunized with tetanus toxoid (TT) are able to produce a specific antibody response and whether oral treatment with retinyl palmitate, concurrent with immunization, affects the magnitude of the anti-TT response. When rats aged 8-15 d and nursed by vitamin A-sufficient dams were immunized with TT, no primary anti-TT immunoglobulin (Ig) M or IgG response was detected. However, nursling rats formed immunologic memory to TT because, when they were reimmunized at 40 d of age, their secondary anti-TT IgG response exceeded the primary response of 40-d-old vitamin A-sufficient rats (P < 0.02). Provision of retinyl palmitate (equal to 37.5 or 150 micrograms retinol equivalents) by mouth with early primary immunization did not change the magnitude of the secondary anti-TT IgG response. However, the age of nursling rats at first immunization significantly affected the magnitude of their secondary anti-TT IgG response, because rats first immunized at 15 d of age and reimmunized at 40 d of age produced a secondary response that was nearly fivefold greater than that of rats immunized at 8 and 40 d of age. In conclusion, nursling rats immunized with TT formed immunologic memory, which was affected significantly by the timing of the primary immunization. However, the administration of retinyl palmitate concurrent with early primary immunization did not significantly affect the development of memory to TT.