Feline ocular and cerebrospinal fluid Toxoplasma gondii-specific humoral immune responses following specific and nonspecific immune stimulation

Toxoplasma gondii-naive cats and cats previously infected orally with T. gondii tissue cysts were inoculated with soluble tachyzoite antigens plus adjuvant or adjuvant alone. Toxoplasma gondii-specific IgM and IgG were measured in serum, aqueous humor, and cerebrospinal fluid (CSF). The Goldman-Witmer coefficient (C value) for ocular or central nervous system (CNS) antibody production was calculated for aqueous humor or CSF samples positive for T. gondii-specific antibodies. Following inoculation with adjuvant plus soluble tachyzoite antigens, ocular and CNS T. gondii-specific IgG C values increased in the three previously infected cats. Following inoculation with adjuvant, the two previously infected cats had increases in ocular and CNS T. gondii-specific IgG C values. Ocular (23 cats) or CNS (13 cats) T. gondii-specific IgG C values of over 1 were detected in some T. gondii-naive cats following inoculation with adjuvant plus soluble tachyzoite antigens. The results of this study suggest that T. gondii-specific IgG C values of over 1 in aqueous humor or CSF do not prove active ocular or CNS infection in all cats.