T-dependent antigens are more immunogenic in the subarachnoid space than in other sites.

Systemic antibody responses were compared in mice injected with antigens into the subarachnoid space (SAS) and into conventional sites. Introduction of T-dependent antigens into the SAS induced higher systemic antibody responses than injections into any other sites. This applied to both soluble and particulate antigens and was more apparent in secondary than in primary responses. The effect was not observed with a T-independent antigen and not consistently with high doses of sheep red blood cells (SRBC). It was concluded that the subarachnoid space is a highly efficient site for the induction of systemic antibody production, in particular to low amounts of T-dependent antigens.