We suggest a method for detection of highly conductive surface electron states including topological ones. The method is based on measurements of the photoelectromagnetic effect using terahertz laser pulses. In contrast to conventional transport measurements, the method is not sensitive to the bulk conductivity. The method is demonstrated on an example of topological crystalline insulators Pb1−xSnxSe. It is shown that highly conductive surface electron states are present in Pb1−xSnxSe both in the inverse and direct electron energy spectrum.

We demonstrate that measurements of the photoelectromagnetic effect using terahertz laser radiation may provide a unique opportunity to discriminate between the topological surface states and other highly conductive surface electron states. We performed a case study of mixed (Bi -x 1 In x ) 2 Se 3 crystals undergoing a topological phase transformation due to the transition from the inverse to the direct electron energy spectrum in the crystal bulk at variation of the compositionx. We show that for the topological insulator phase, the photoelectromagnetic effect amplitude is defined by the number of incident radiation quanta, whereas for the trivial insulator phase, it depends on the power in a laser pulse irrespective of its wavelength. We assume that such behavior is attributed to a strong damping of the electron-electron interaction in the topological insulator phase compared to the trivial insulator.

The technique o f elution b y pronase of murine immune lymph node cells adherent to relevant allogeneic target cells has been developed for enrichment of effector T cell population. A fraction of killer cells has been obtained possessing cytotoxic activity which exceeds that of the initial immune lymphocyte population b y a factor of 6-8 as judged by a number of lymphocytes required for 50 % cytotoxic effect (CE). T h e gain in CE is fairly reproducible in different H-2 systems and under various lymphocyte-target incubation conditions. It appears to be due t o the quantitative enrichment of the population in cells bearing receptors to the particular H-2 antigens and giving rise to specific CE rather than t o an increase in cytotoxic activity per cell resulting from treatment with the target monolayer and pronase. The eluted killer cell fraction is characterized by a twofold increase in percentage of cells killed by anti-@ antibody, a 4-5-fold increase in the number of DNA-synthesizing cells and b y an increase in medium and largc lymphocyte content. A further enrichment in effector lymphocytes is reached by depletion of B cells a t the expense of their receptors t o Fc fragment of Ig. Macrophage monolayer fixed by glutaraldehyde lost its capacity t o absorb effector lymphocytes. T h e implications of the data obtained for further studies o n cell-mediated immunity are discussed. 1 I ] and the rosetteHowever, one should not disregard the possibility that in all the above-mentioned cases passive absorption of Ig on the T cell surface is revealed rather than its true (endogenic) receptors. In fact, receptors to both F c fragment of IgM Label release upon incubation with immune and normal lymphocytes EA: Erythrocytes-antibodies 281 the possibility is not excluded that such antibodies are actually produced by small B cell contaminants present in suspension. Experimental analysis [29, 301 of these and other ambiguous points in the interpretation of such results have raised doubts whether the above cited reports really concern the endogenic T receptors. .Introduction'Meanwhile, T cell receptors responsible for interaction with target cells (TC) in the H-2 system have been shown to differ from Ig of the known classes [31-331. Such receptors are manifested in the ability of cytotoxic lymphocytes t o get selectively attached for several hours at 25-37 OC t o the naturally immunosorbent-monolayer of the relevant TC ' [34-361. To study the properties o f the effector T cells, including the nature of their receptors specific to the H-2 antigens, it seems t o be essential t o isolate these cells from the whole population where they occur in a ratio of 1-4 ' %, [ 3 7 -~3 9 ] , and to concentrate them.The present work describes a technique developed for the enrichment of the effector T lymphocyte population in cells reactive to the particular H-2 antigens. T h e ability of pronase to completely and reversibly prevent immune lymphocytes from absorption on T C monolayer with no damage of the latter described earlier [40] is t...

Optimum conditions were selected for testing of direct and indirect H‐2 reactive rosette‐forming cells (RFC) with the use of sheep or mouse erythrocytes coated with soluble H‐2 antigens. Rosette formation with mouse erythrocytes is shown to be an immunologically specific reaction and to be inhibited by the pretreatment of cells with the corresponding soluble H‐2 antigen preparation. Rate of killer cell and RFC formation is different after primary and secondary immunization with an allogeneic tumor, Unlike killer cells. RFCs are inactivated without complement by rabbit antibodies against mouse γ‐globulin (MGG). In contrast to killer cells, which are eliminated in the presence of complement by anti‐θ antibodies but not by anti‐plasma cell antigen (PC.1) and anti‐MGG antibodies, direct RFCs are not inactivated by anti‐θ but are eliminated partiallv by anti‐MGG and anti‐PC1. The RFCs are shown to be concentrated in the low‐density fractions of the discontinuous bovine serum albumin gradient, whereas cytotoxic lymphocytes are distributed less closely, being concentrated in the intermediate fraction, which does not differ morphologically from the initial cell suspension. Killer and rosette‐forming cells reactive to the same H‐2 antigens appear to be two non‐overlapping populations of T and B cells, respectively, and no T‐B cooperation is required for destruction of target cells.